Fabio Fulchini

Mojtaba Ghadiri
email: m.ghadiri@leeds.ac.uk

Antonia Borissova

Benjamin Amblard

Stéphane Bertholin

Mahdi Ann Cloupet

Stephane Bertholin

Development of a methodology for predicting particle attrition in a cyclone by CFD-DEM

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

INTRODUCTION

Fluidised beds and circulating fluidised beds are widely used for carrying out heterogeneous catalytic reactions in which the solid catalyst particles need to be regenerated in order to be reprocessed. The circulation of the solids subjects them to mechanical stresses causing attrition. The fines that are generated in this way pose significant process problems and considerable material losses. Zenz [1] identifies the most stressful regions in a fluidised bed,

where the mechanical stresses lead to particle attrition, as the gas distributor jets, bubbling bed, cyclones and bends. He also suggests that each of these sources of attrition should be analysed individually, due to the different mechanisms of attrition involved, such as surface abrasion, chipping and fragmentation. The predominance of any of these mechanisms is affected by a combination of particle properties and process operating conditions as well as the geometry of the unit [START_REF] Welt | Catalyst attrition and deactivation in fluid catalytic cracking system[END_REF]. The cyclone is one of the most significant contributors to particle attrition especially at high superficial gas velocities [START_REF] Werther | Catalyst Attrition in Fluidized-Bed Systems[END_REF]. Particles entering the cyclone at high velocities are likely to impact on the opposite side of the inlet duct, and slide against the wall towards the bottom outlet. Usually particle attrition in cyclones is by surface abrasion/chipping, but whenever a certain threshold velocity is exceeded then fragmentation can also take place. Werther et al. [START_REF] Werther | Catalyst Attrition in Fluidized-Bed Systems[END_REF] developed a model of cyclone-induced particle attrition under conditions of surface abrasion for the Fluid Catalytic Cracking (FCC) catalyst particles.

They reported that the attrition rate was dependent on the material properties, gas kinetic energy, and particle size and inversely proportional to the square root of the particle loading due to the 'cushioning' effect. Reppenhagen et al. [START_REF] Reppenhagen | Catalyst attrition in cyclones[END_REF] examined the validity of the model by testing nine different cyclone geometries. Their model is based on pure abrasion but, as noted by Werther et al. [START_REF] Werther | Attrition[END_REF], if the inlet velocity is increased and/or the particle loading decreased, particles will undergo severe chipping and/or fragmentation especially in case of fresh catalysts, which very often have some mechanical weaknesses like surface asperities, inhomogeneity of the matrix, etc.. However, in normal operations, conditions leading to severe particle attrition are usually avoided by using an appropriate design of the cyclone.

Nevertheless, the development of a model that can predict the extent of attrition is highly desirable. It is critical to understand the conditions under which a certain mechanism of attrition is dominant. The particle dynamics in a cyclone is the key to understanding this phenomenon. Chu et al. [START_REF] Chu | CFD-DEM simulation of the gassolid flow in a cyclone separator[END_REF] carried out a CFD-DEM analysis of the gas-solids flow in a cyclone, showing that the loading of particles can affect the particle trajectory pattern as well as the magnitude of interparticle and particle-wall interactions, the latter being dominant for particle loading less than 0.5 kg Solid /kg Air . In such cases, for instance, particle collisions against the wall of the cyclone can be the main cause of attrition. Reppenhagen et al. [START_REF] Reppenhagen | Catalyst attrition in cyclones[END_REF] confirmed that particle attrition in cyclones is the consequence of high velocity collisions at the entrance against the wall by looking at the erosion of a black-leaded film on the inner wall of a cyclone. Additionally, particles are also inevitably subjected to shear along the cyclone wall.

For a given solids loading, factors that contribute to cyclone attrition are the cyclone fluid dynamics, which dictates the particle velocity and residence time and the particle physical properties which influence the dependence of attrition on the operating conditions. Coupling the dynamics of particle motion with a single particle breakage model can give an estimate of the cyclone attrition, as proposed by Ghadiri et al. [START_REF] Ghadiri | Attrition of FCC powder in the jetting region of a fluidized bed[END_REF] for predicting the attrition of FCC particles induced by a single jet in a fluidised bed. This work aims to emulate this approach by obtaining the particle dynamics in a cyclone by a four-way-coupling CFD-DEM simulation. The impact breakage of crushed manganese oxide particles, intended for use in the Chemical Looping Combustion (CLC) process, is evaluated experimentally by single particle impact testing in order to develop a single particle breakage model that is used, along with the model of surface wear of Archard [START_REF] Archard | Contact and Rubbing of Flat Surfaces[END_REF], to calculate the overall particle attrition in a cyclone.

The calculation is performed in the simulation post-processing stage using the time-averaged values of the frequency of particle-wall and particle-particle collisions, the particle relative impact velocity, the number of collisions per particle, the normal compressive force acting on the particles and the particle sliding distance along the wall per region of interest of the cyclone. The cyclone is partitioned into 10 regions of interest for particle motion in order to predict attrition locally.

As stated above, the test material is made of crushed manganese oxide particles intended for use as oxygen carrier for the CLC process. An impact breakage model is developed for a wide range of particle impact velocities and for different size cuts based on the single particle impact test method [START_REF] Zhang | Impact attrition of particulate solids. Part 2: Experimental work[END_REF], thereafter referred to as 'SPIT', and by the Scirocco Impact Test method [START_REF] Bonakdar | A method for grindability testing using the Scirocco disperser[END_REF], termed as 'SIT'. The outcomes of the two tests are combined and a single particle attrition model is presented based on the theoretical chipping model of Ghadiri and

Zhang [START_REF] Ghadiri | Impact attrition of particulate solids. Part 1: A theoretical model of chipping[END_REF].

MATERIALS AND METHODS

The material, provided by IFP Energies Nouvelles in Solaize, France, consists of a batch of fresh natural manganese ores crushed for use as CLC oxygen carriers which will be denoted as F-CLC (i.e. fresh CLC particles). The particle size distribution (PSD) is wide and the particle shape is irregular as shown in Figure 1. The particle envelope density is 3300 kg/m 3 .

The PSD is evaluated gravimetrically by sieving using German standard DIN 4188 sieves.

The five most representative size cuts of the distribution are chosen for impact testing to establish the effect of particle size. The material is very dusty as shown in Figure 1. In fact, dust readily adheres to particles and this affects the breakage results, as it contributes to the mass of debris. Therefore, before the tests, in order to get rid of these fines, the powder is 'washed' by wet sieving using water, which does not dissolve manganese oxide, and later on dried in an oven. Later experimental inspection showed no weakening of the particles due to washing as its breakability is slightly lower than that of the non-washed material. The washed material is termed as W F-CLC.

The two impact test methods, i.e. single particle impact test (SPIT) [START_REF] Zhang | Impact attrition of particulate solids. Part 2: Experimental work[END_REF] and Scirocco impact test (SIT) [START_REF] Bonakdar | A method for grindability testing using the Scirocco disperser[END_REF] allow the particle extent of breakage to be correlated with its impact velocity.

Generally, the extent of breakage is defined as the ratio of the mass of fines produced by attrition to the total mass of particles. Moreover, the theoretical model of Ghadiri and Zhang [START_REF] Ghadiri | Impact attrition of particulate solids. Part 1: A theoretical model of chipping[END_REF] for chipping of semi-brittle materials is used to model the experimental data. Further single particle impact tests are carried out on the 'non-washed' powder, F-CLC, and also used to investigate the effect of angle of impact.

In parallel, a CFD-DEM simulation of a small scale Stairmand cyclone is performed using EDEM TM and ANSYS Fluent software packages (DEM Solutions, Edinburgh) to evaluate the fluid-particle interactions therein. In the post-processing analysis the time-averaged values of the frequency of particle-wall and particle-particle collisions, velocity and angle of collisions, the number of collision per particle, compressive force acting on the particles and sliding distance are calculated. The cyclone is partitioned into 10 regions, where the dominant particle dynamics, i.e. collision or sliding against the wall is identified. The above-mentioned parameters are then obtained for each of these regions. Combining them with the experimental model of impact breakage and the abrasive model of Archard [START_REF] Archard | Contact and Rubbing of Flat Surfaces[END_REF] allows the extent of particle attrition to be predicted.

Particle Size Distribution

The particle size distribution of F-CLC is evaluated by mechanical sieving and reported in Figure 2. The material is first split to get a small representative sample, sufficient for sieving, and avoiding errors due to segregation by size due to transportation of the initial large batch. F-CLC representative size cuts F-CLC mechanical sieving

Breakage Analysis

Erosive and abrasive wear are two mechanisms of small-scale surface material removal. The former results from particle collisions, and the latter from particle sliding or rolling. The particle collisional breakage is analysed experimentally for F-CLC and W F-CLC particles by two different techniques: SPIT (single particle impact test) [START_REF] Zhang | Impact attrition of particulate solids. Part 2: Experimental work[END_REF] and SIT (Scirocco disperser) [START_REF] Bonakdar | A method for grindability testing using the Scirocco disperser[END_REF].

The procedure for calculating the extent of breakage is described below in equations 2-4. Due to potential loss of particles during handling and testing, there is some uncertainty in estimating the actual extent of breakage. So upper and lower limits of breakage can be defined as follows. The initial mass of material, m 0 , is equal to:

0 m d e l o s s m m m m    ( 1 )
where m m is the collected mass of mother particles, m de is the collected mass of debris and m loss is the mass loss.

Ghadiri and Zhang [START_REF] Zhang | Impact attrition of particulate solids. Part 2: Experimental work[END_REF] define the extents of breakage as R -, R + and R * for the cases in which the losses are attributable to mother particles, debris or neglected. In the last case, the relative contributions of the mother particles and debris to the losses are uncertain, so R * is based on the collected material after the impact test.

de

0 m R = m ( 2 ) + 0 m 0 m -m R = m ( 3 ) * de de m m R = m + m ( 4 )
In practice R * is close to R -and for the case in which the losses are small, the gap between R - and R + is small. Since the SPIT and SIT methods have different degrees of losses, in this work the average of R -and R + , denoted as R avg , is used.

Mother particles and debris are collected after the test and separated using a sieve, the size of which is two standard sieve sizes below the lower limit of the feed particle size; e.g. the debris originating from breakage of particles of sieve cut, d 0 =355-400 µm, is separated using a sieve with a mesh size of d s =300 µm. This technique has been widely used to quantify particle breakage by chipping when the debris is much smaller in size than the mother particles, so that the choice of the sieve size is actually not critical in the determination of the mass of debris [START_REF] Yuregir | Observations on impact attrition of granular solids[END_REF][START_REF] Kwan | Development of a novel approach towards predicting the milling behaviour of pharmaceutical powders[END_REF]. Naturally, this method is only valid up to the point where the size of mother particles d m decreases to a critical size d m,min , which is equal to the size of the sieve opening d s of the sieve used for separating the debris from the mother particles as shown in Figure 3. The extent of breakage under these conditions is referred to as R max and, considering spherical particles, can be calculated as follow:

3 3 de,max 0 m,min m,min m,min s max 0 0 0 0 0 m m m m d d R 1 1 1 m m m d d                      ( 5 )
Beyond this theoretical limit there is no more distinction between mother particles and debris.

R max is then the maximum value of the extent of breakage for which the above approach can be used for describing the extent of breakage by chipping. On the other hand, it can also be seen as the threshold from chipping to fragmentation, which occurs when the particle breaks into several pieces of comparable sizes or at least when there is no clear distinction between mother particle and the rest. R max is shown in Table 1 for all the size cuts used in this work. The experimental data are fitted according to the chipping model of Ghadiri and Zhang [START_REF] Ghadiri | Impact attrition of particulate solids. Part 1: A theoretical model of chipping[END_REF] for semi-brittle material failure mode, given by equation 6.

2 G&Z p c H R = ρ d K 2 G&Z p p α v (6)
where G& Z α is a proportionality constant, H and K c are respectively hardness and fracture toughness, ρ p is the particle density, d p is the particle size and v p the particle impact velocity.

As for the abrasive wear due to particles sliding against the wall of the cyclone, the model of Archard is used which relates the extent of breakage, Ar R , to the hardness of the particle H, its sliding distance Δs, normal compressive force acting on it, F n , and a proportionality

constant Ar  . n Ar Ar F s R H    ( 7 )
Δs and F n are obtained for each contact from outputs of the simulation. The hardness, H, is evaluated experimentally for several CLC particles using the nano-indentation technique. The Berkovich indenter is used at the loading rate of 5 mN/s for maximum loads of 25, 50 and 75 mN. H is found to be equal to 5.2 GPa with a coefficient of variation of 9%. No experimental data are available for wear due to particle sliding. So, considering the scale of the group n F s H  , the proportionality constant Ar  is chosen to have a value (10 12 ) such that Ar R is comparable

in magnitude with G & Z R
. This is obviously arbitrary, but the main focus here is on the development of methodology. Realistic values are material dependent.

Single Particle Impact Test (SPIT)

The SPIT is carried out according to the procedure described by Ghadiri et al. [START_REF] Ghadiri | Attrition of FCC powder in the jetting region of a fluidized bed[END_REF]. As shown in Figure 4, the particles impact against a target of sapphire while their velocities are monitored. The tests are carried out at impact velocities of about 1.5 m/s (free fall), 8, 14, 20 and 26 m/s. In order to shed light on the effect of impact angle θ, inclined targets with angles of 30°, 45° and 60° as shown in Figure 5 are also used. F-CLC and W F-CLC particles are both used to characterise the extent of breakage as a function of size and impact velocity, while F-CLC of 355-400 µm size cut is also furtherly used to analyse the effect of impact angle. The following impact velocities are used for all tests: 2, 8, 14, 20, 26 m/s.

Scirocco Impact Test (SIT)

Scirocco is the dry disperser unit of Malvern Mastersizer 2000. Particles are fed and dispersed by an eductor using a high pressure nozzle operating in the range of 0.1 to 4 barg. Given the 'L'-shape bend of the eductor, particles impact and experience stress causing attrition.

Following passage through the disperser the particles are presented to the laser diffraction instrument for size measurement. They are then recovered downstream of the instrument by a plastic, axial cyclonic dust collector. The material is eventually collected and the extent of breakage characterised. The shift in PSD due to attrition can be obtained by both laser diffraction and gravimetric analysis. Given the design of the axial cyclone, the particles can avoid high velocity impacts at the entry. For this reason, its contribution to attrition is assumed to be far less than that caused by the high impact velocities achieved by SIT.

Varying the nozzle pressure from 0.1 to 4 barg for CLC particles, it is possible to achieve a range of impact velocity in Scirocco from 18 to 62 m/s, depending on their size. The experiments are performed on W F-CLC with the test details given in Table 2.

The particle velocity at the first impact in the Scirocco is calculated knowing the particle size, density and nozzle pressure, based on the correlation developed by Ali et al. [START_REF] Ali | Particle Breakage in a Scirocco Disperser[END_REF], who simulated the gas-solid behaviour in Scirocco using Lagrangian particle tracking for the discrete phase and the Eulerian approach for the fluid. phase, so that Newton's third law of motion is satisfied [START_REF] Xu | Numerical simulation of the gas-solid flow in a fluidized bed by combining discrete particle method with computational fluid dynamics[END_REF]. In this case, the fluid flow field is recalculated every 25 time steps of the DEM. A small scale Stairmand cyclone with tangential inlet style is used as the reference geometry in the simulation [START_REF] Haig | An empirical investigation into the in fl uence of pressure drop on particle behaviour in small scale reverse-flow cyclones[END_REF]. The dimensions, according to Figure 6, are reported in Table 3. The computational fluid domain contains 90,793 tetrahedron cells of average length of 1.35 mm. The Reynolds Stress Model (RSM) is used to solve the fluid-dynamics of the system as it gives the best agreement with experimental measurements [START_REF] Xu | Numerical simulation of the gas-solid flow in a fluidized bed by combining discrete particle method with computational fluid dynamics[END_REF][START_REF] Haig | An empirical investigation into the in fl uence of pressure drop on particle behaviour in small scale reverse-flow cyclones[END_REF][START_REF] Hu | Studies on strongly swirling flows in the full space of a volute cyclone separator[END_REF]. The boundary conditions are set for the fluid entry and exit. Air enters the cyclone at 40 m/s while atmospheric pressure is set for both top and bottom outlets. The drag model for a single sphere is used. The particles are spheres of 755 µm diameter and a density of 3300 kg/m 3 . It should be noted that the particle size is not the actual one of the test material for which the experimental breakage data have been obtained. The use of such large particle size reduces the simulation time. However, as the effect of particle size is known from the impact breakage model, the extent of breakage for 755 µm is used in the calculations. Other DEM parameters, i.e. the shear modulus, Poisson's ratio and coefficients of restitution, sliding friction and rolling friction are 0.1 GPa and 0.25 and 0.5, 0.5, 0.01, respectively. It should be noted that these are not the actual values for this specific material at hand, but rather typical values which are realistic. The number of particles generated per second at the inlet pipe is 4000, with an initial velocity of 1 m/s, which results in a mass flow rate of 2.97 g s -1 and a solids to fluid mass ratio (solids loading) of 0.31 kg solids /kg air . The DEM integration time step is 1.5x10 -6 s for a total simulation time of 4 s.

RESULTS AND DISCUSSIONS

Impact breakage analysis results of Single Particle Impact Test (SPIT) and

Scirocco Impact Test (SIT)

Recalling the model of Ghadiri and Zhang [START_REF] Ghadiri | Impact attrition of particulate solids. Part 1: A theoretical model of chipping[END_REF], the experimental results, in terms of extent of breakage, are plotted versus ρ p d p v p 2 in order to work out propensity and is often referred to as 'breakability index' [START_REF] Ghadiri | Impact attrition of particulate solids. Part 1: A theoretical model of chipping[END_REF]. It allows a direct comparison of the breakability of different materials upon impact. For F-CLC particles the extents of breakage R + , R * , R -for all tested size cuts are reported in Figure 7, while the average value R avg is shown in Figure 8. Extent of breakage Ravg for F-CLC particles by the SPIT for all particle sizes plotted against ρpdpvp2 A good unification of the data points is achieved confirming the model takes proper account of particle size and impact velocity. It should also be noted that the maximum extent of breakage is around 4%, which is well below R max , supporting that observational evidence that particles undergo chipping. Further analysis on the effect of the angle of impact, θ, indicates a simple linear dependency of the extent of breakage with the sinθ, as shown in Figure 9. Remarkably, all the data points at normal and inclined impact lie on the same straight line.

The model of Ghadiri and Zhang [START_REF] Ghadiri | Impact attrition of particulate solids. Part 1: A theoretical model of chipping[END_REF] is then modified to take account of the angle of impact empirically, as shown below:

2 2 G&Z G&Z p p p c H R =α ρ d v sin K  ( 8 )
where

2 G&Z c F CLC H α K  is equal to 4.0×10 -5 .
The transition impact velocity for a given particle size below which there is little/no breakage, v p0 , can be calculated considering the intercept of the fitted line with abscissa, i.e. the coordinate point (ρd p v p0 2 , 0). In this case ρd p v p0 2 is negative and equal to -3.81/0.40. This would return a negative value of the square of transition velocity, which is not physically possible but is a sign that the breakage of non-washed material is a little overestimated, as the adhered dust comes off the particles too.

Therefore, the transition velocity is calculated instead from the results obtained for the 'washed' particles (W F-CLC). The results of W-F-CLC from SPIT and SIT are reported separately for all size cuts in terms of R + , R * , R -in Figure 10 and Figure 11, respectively.

They are also put together and shown in Figure 12, where a remarkable unification is obtained. By extension, the dependency on the angle of impact is implemented in the model for the 'washed' material, defining the extent of breakage as R W F-CLC :

2 2 W F-CLC G&Z p p p c W F CLC p p 0 H R α d v sin K v v           ( 1 0 )
The values of the transition velocities for the studied size cuts and the particle size, for a normal impact, are reported in Table 4. The impact of several particles of W F-CLC at free fall velocity (about 1.5 m/s) is analysed by using a high-speed camera, confirming that breakage occurs at such low impact velocities. A sequence of photos is reported below, showing breakage upon impact of a particle of 355-400 µm (Figure 13). A comparison of extents of breakage of F-CLC and W F-CLC is shown in the Appendix in Figure A1.

Figure 13. A W F-CLC particle breaking upon impact at 1.5 m/s

CFD-DEM Simulation of a Cyclone

A steady state CFD study of the fluid dynamics without particles is initially performed and compared with that obtained from the CFD-DEM simulation, where particles are also simulated. The axial, radial and tangential velocities for both cases are reported in Figure 14 for the y-plane containing the diameter with the coordinate system shown in the figure. The CFD-DEM simulation reveals the necessity of evaluating attrition locally as the particles experience high velocity impacts, mostly at the entrance, as well as shear thereafter. Attrition should therefore be analysed locally based on the current state of the particles, given by EDEM TM as the geometry of the cyclone is partitioned into 10 regions of interest, as shown in Figure 16. The information obtained by the software such as particle velocity, number of particles, particle displacement and normal compressive force are then used to work out the particle attrition occurring in each region. Referring to Figure 16, the 'Inlet' is the region that corresponds to the feeding pipeline. In this region attrition is neglected as a result of minimum, perhaps null, inter-particle and wallparticle interaction.

In the region called 'Impact' particles collide at the highest velocity mainly against the wall of the cyclone. The particle attrition here, for both particle-wall and particle-particle collisions, is evaluated applying the model of chipping of Ghadiri and Zhang [START_REF] Ghadiri | Impact attrition of particulate solids. Part 1: A theoretical model of chipping[END_REF], R G&Z , fitted to the experimental data. The regions "Shear 1" to "Shear 8" are all the same z-length as 20 mm.

Here, attrition is evaluated applying the abrasive wear model of Archard [START_REF] Archard | Contact and Rubbing of Flat Surfaces[END_REF], R Ar , given the tendency of particles shearing along the wall of the cyclone. In "Shear 1" collisional attrition is also evaluated, being a transition region.

Cyclone attrition analysis

Particle attrition is evaluated under steady state condition, i.e. the inlet solids flow rate is equal to outlet solids flow rate. This occurs after a time equal to the particle residence time; its time-averaged value is equal to 1.35 s, implying a plug flow behaviour, while the time-averaged number of particles inside the cyclone is 5424, as shown in Figure 17. At steady state, the simulation returns the following time-averaged parameters per region 'i':

the number of particles N pi , the net flow of number of particles i p N  , the number of particle- wall and particle-particle collisions N ci , the particle relative impact velocity Δv pi , the particle velocity v pi , the compressive normal force F ni and the angle of impact θ i .

The extent of particle attrition (mass fraction of debris produced) in the "Impact" region, R Impact , is evaluated as the summation of two contributions arising from particle-wall and particle-particle collisions, where the latter is calculated considering that an impact between two particles leads to the same breakage as of one particle impacting against a fixed target at their relative impact velocity:

PW PW PP PW c/p Im pact W F-CLC c/p c W F-CLC c N R R N R 2     (11)
According to equation ( 11) R w F-CLC is the impact breakage model for W F-CLC particles computed using the relative particle-wall or particle-particle velocity and angle of impact,  is the collision efficiency factor (it takes into account the fact that some collision might not occur above the transition velocity).

c / p N is calculated according to equation [START_REF] Ghadiri | Impact attrition of particulate solids. Part 1: A theoretical model of chipping[END_REF], as the ratio of the frequency of collision with the flow rate of number particles entering the "Impact" region; at steady state this is equal to that entering the cyclone (4000 s -1 ):

Impact Impact 0 c c c/p p p N N N N N       (12)
The frequency of collision in the "Impact" region is calculated as the total number of collisions, divided by the total time of observation, as shown in equation ( 13):

Im pact Im pact c c N N t    (13) while c
 is calculated according to equation ( 14) as the ratio of number of collisions above the transition velocity over the total number of collisions:

Im pact p p0 Im pact c v v c c N N     ( 14
)
Collisional attrition is furthermore evaluated for the region "Shear 1" being a transition region between a collision dominant mechanism to surface abrasion.

On the other hand, particle attrition for the shearing regions shear ,i R is evaluated as

shear ,i Ar ,i R R  (15)
Recalling the definition of Archard's model, the particle sliding distance against the wall, Δs i , is calculated as:

i i p i s v    ( 1 4 6 )
where τ i is the mother particle residence time per region, given by The time-averaged compressive force per particle and sliding distance are reported below in Figure 18, showing the maximum value in regions 'Shear 1' and 'Shear 3', respectively. All the values mentioned above are reported in the Appendix in Table A1 along with the extent of breakage per region R i and the cumulative extent of breakage cum,i R , which is defined as

n n cum,i i i i 0 i 0 R 1 (1 R ) R        ( 1 6 8 )
where 'n' is the number of regions.

In Figure 19 the extent of breakage per region R i and the cumulative extent of breakage cum R are plotted showing that the 'Impact' region along with the 'Shear 1' region provide together the largest contribution to attrition, about 81% of the total breakage. Moreover, the particle size at each region, d pi , is calculated as:

1/3 p,i 0 cum,i d d (1 R )   (19)
and finally, the breakage rate per region, r i , is according to the equation ( 21):

i i1 p , i i r m N R    (170)
The particle size and the breakage rate at each region are reported in Figure 20. The figure shows an abrupt reduction in particle size related to the passage in the "Impact" region and the first shearing region, where the particle velocity is more important. Then a more gradual reduction as the particles head to the last shear region. It should be noted that these results are based on an arbitrary parameter for the Archard model, therefore no comparison with a real system can be made. However, the trend as well as the magnitude of particle attrition for this kind of system appears realistic: after one passage through the cyclone, the diameter of a particle is reduced only by 0.03% (from 755 µm to 754.8 µm).

A more detailed analysis of the regions "Impact" and "Shear 1" is reported in Figure 21 and Table 5 in order to elucidate the underlying mechanism of attrition.

Figure 21. Extents of breakage, R, and collision efficiency factor, η c , of the regions "Impact" (in green) and "Shear 1" (in orange) as a result of surface abrasion, particle-wall and particle-particle collisions At first, it can be concluded that the region "Shear 1", where there is the transition from collisional attrition to surface abrasion by shear, attrition is caused by surface abrasion only, although there is still a number of particle-wall collisions per particle. Practically all the collisions in this region occur at velocities lower than the transition velocity. In general, all the collisions occurring from region "Shear 1" downwards are below this limit.

As discussed above the "Impact" region is the main source of attrition in the cyclone. In particular, particle-wall collisions are the main cause leading to 72% of attrition of the region and 42% of the overall cyclone attrition. The particle-wall and particle-particle impacts occur in both cases at very steep angles, respectively at 27° for and 34° with a relative impact velocity of about 2.7 m/s. The collision efficiency in both cases is high and nearly equal to 93%. All the previous features being comparable, the number of collisions per particle is accountable for the difference in terms of attrition between the two cases. In fact, as reported in Table 5 a particle in the "Impact" region collides about 1.9 times with the wall but only 0.2 times with another particle. This occurrence is expected from a low solid loading case like ours.

More case studies at different solids loading and inlet velocity are required to elucidate the interplay between the attrition caused by particle-wall and particle-particle collisional and surface abrasion.

CONCLUSIONS

Particle attrition in a cyclone has been analysed by the CFD-DEM method using single particle breakage models of impact and shear. A conventional Stairmand cyclone design is used at low solids loading, where the particle-wall interactions causing attrition are dominant.

When the particles enter the cyclone at a high velocity they experience an initial breakage upon impact on the cyclone walls. Subsequently they flow spirally downwards and experience abrasive wear due to sliding along the walls. The chipping model of Ghadiri & Zhang is fitted to the breakage data of CLC particles, measured using two types of single particle impact tests. Archard's model of abrasive wear is used to simulate the abrasive wear caused by particle shear against the walls. The CFD-DEM simulation is performed using spheres of 755 μm diameter and the same density as CLC particles, with a solid loading of 0.31 kg solid /kg air and an inlet air velocity of 40 m/s. The simulation quantified the relative contributions of the particle collisional and sliding behaviour in the cyclone. The breakage models are then coupled with the information obtained from the simulation in terms of particle dynamics. The overall attrition extent in the cyclone is then calculated and described as a function of the particle mechanical properties and process conditions. The major contributors to attrition are the entrance region and the initial sliding region, contributing around 81% of the total attrition where both collisions and sliding are dominant, as compared to further downstream regions.

The overall cyclone attrition is therefore shared between particle-wall collisions, 42%, particle-particle collisions 16% and surface abrasion by shearing 42%. A methodology is therefore presented for identifying the relative importance of various regions in the cyclone in causing attrition and predicting the extent of attrition based on the mechanical properties of the particles and the dynamics of particle flow in cyclones.

APPENDIX

  Abbreviation CLC Chemical Looping Combustion F-CLC Fresh CLC particles PP refers to particle-particle interactions PW refers to particle-wall interactions W F-CLC Washed fresh CLC particles SPIT Single particle impact test SIT Scirocco impact test G&Z Ghadiri & Zhang Ar Archard i refers to a region

Figure 1 .

 1 Figure 1. Scanning Electron Micrograph of crushed manganese particles used as test material

Figure 2 .

 2 Figure 2. Particle Size Distribution of fresh CLC particles by mechanical sieving and most representative size cuts used for experimental analysis (in red) The most representative size cuts are chosen to carry out the impact tests, they are: 180-212, 212-250, 250-280, 300-355 and 355-400 µm.

Figure 3 .

 3 Figure 3. Schematic representation of the limit of the separation between mother particles and debris

Figure 4 .

 4 Figure 4. Schematic of the Impact test rig, [8]

Figure 5 .

 5 Figure 5. Angle of Impact

20. 6 Figure 6 .

 66 Figure 6. Dimensions of the cyclone The CFD-DEM simulation of a cyclone is carried out by coupling ANSYS-Fluent with EDEM TM . DEM modelling is at the individual particle level, while the fluid flow by CFD is at the computational cell level. The four-way coupling allows the fluid forces to act on particles, particles interact with each other and react to and influence the fluid motion. At each time step, DEM gives the information such as velocities and positions of individual particles, for the evaluation of porosity and volumetric fluid-particles interaction forces in a computational cell. CFD uses them to determine the fluid flow field, which then yields the fluid forces acting on individual particles. The resulting forces are then incorporated into DEM, and individual particle motion is calculated in the next time step. The particle motion in turn affects the fluid

  of the line. It is regarded as a lumped parameter that takes account of the mechanical properties and represents the breakage

Figure 7 .Figure 8 .

 78 Figure 7. Extents of breakage R+, R* and R-for F-CLC particles by the SPIT for all sizes plotted against ρ p d p v p 2 .

Figure 9 .

 9 Figure 9. Extent of breakage R for F-CLC particles by the SPIT for all sizes and angles of impact plotted against ρ p d p v p 2 sinθ

Figure 10 .Figure 11 .Figure 12 . 2 For

 1011122 Figure 10. Extents of breakage R+, R* and R-for W F-CLC particles by the SPIT for all the sizes plotted against ρ p d p v p 2 .

Figure 14 .

 14 Figure 14. (a): axial, radial and tangential fluid velocities in the case of a steady state CFD simulation; (b): in the case of a transient CFD-DEM simulation at 4 s

Figure 15 .

 15 Figure 15. Solid pattern in the cyclone

Figure 16 .

 16 Figure 16. Regions of interest of the cyclone

Figure 17 .

 17 Figure 17. Cumulative number of particles versus time: INLET in red, OUTLET in blue and ACCUMULATION=IN-OUT in green

  number of collisions per particle and c

Figure 18 .

 18 Figure 18. Compressive force per particle and sliding distance per region

Figure 19 .

 19 Figure 19. Local, R, and cumulative, R cum , extent of breakage per region

Figure 20 .

 20 Figure 20. Particle size and attrition rate per region

Figure A1 .

 A1 Figure A1. Comparison between non-washed (F-CLC) and washed material (W F-CLC) in terms of extent of breakage R plotted against ρ p d p v p 2 sinθ, obtained by SPIT

  , G. Kelleher, Studies of attrition rates in fluid-particle systems via free fall,

Table 1 .

 1 Cut-off sieve sizes used for mother particles-debris separation for F-CLC

	CLC size cuts [µm]	355-400 300-355 250-280 212-250 180-212
	cut-off sieve size [µm]	300	250	212	180	150
	R max [-]	0.39	0.42	0.39	0.38	0.42

Table 2 .

 2 Particle impact velocity as a function of size and pressure in the Scirocco disperser

	Washed CLC particle velocity (W F-CLC) m/s
	Particle Size [µm]	0.1	1	P [barg] 2	3	4
	355-400	18.8 27.7 36.1 m/s 43.6 m/s 50.4 m/s
	300-355	19.6 28.9 37.6 m/s 45.4 m/s 52.5 m/s
	250-280

Table 3 .

 3 Dimensions of the cyclone in mm

	Inlet							Vortex	Vortex
		Inlet	Inlet	Cyclone	Dust	Cyclone	Cone
	duct							finder	finder
		depth	width	diameter	outlet	height	height
	length							diameter	depth
		a	b	D	B c	H t	H t -h	D x	S
	100	20	10	40	10	160	80	20	30

Table 4 .

 4 Transition velocities at normal impact for different particle sizes, v p0 , for given breakability index,

		2 c H K

Table 5 .

 5 Frequency of collision cN  , number of collisions per particle c/p N , angle of impact  , relative impact

	velocity	p  , collisional efficiency factor c v  , extent of breakage R and rational contribution to the regional
			breakage	i R / R , for regions "Impact" and "Shear 1".
				Impact		Shear 1
					Surface
			PW	PP	Abrasion	PW	PP
		c N  [s -1 ]	7387.81	1119.35	-	37034.40	3857.34
		c/p N [-]	1.85	0.27	-	9.26	0.96
		 [°]	27	34	-	26	13
		p  [m s -1 ] v	2.69	2.74	-	0.61	2.32
		c  [%]	92.5	93.4	-	0.00	0.36
		R [%]	0.038	0.014	0.020	0.00	0.00
		i R / R [%]	72.21	27.79	99.73	0	0.27

Table A1 .

 A1 Output of the simulations and calculated parameters

	Inlet

Impact Shear 1 Shear 2 Shear 3 Shear 4 Shear 5 Shear 6 Shear 7 Shear 8 Output of the simulation

		N	p	158	22	86	956	1077	780	982	579	486	315
		p N  [s -1 ]	4000	3947	3936	3894	3928	3720	3708	2929	3877	5488
		v p [m s -1 ]	2.50	2.71	1.85	1.30	0.85	0.77	0.63	0.53	0.52	0.51
		F n_p [µN]	-	-	25.96	1.34	0.49	0.53	0.36	0.52	0.67	1.37
		τ [s]	0.04	0.01	0.02	0.25	0.27	0.21	0.26	0.20	0.13	0.06
	calculated	Δs [m] R i x10 3 [-] R cum x10 3 [-]	--0	-0.524 0.524	0.04 0.202 0.726	0.32 0.083 0.808	0.36 0.034 0.842	0.16 0.017 0.859	0.17 0.011 0.870	0.11 0.011 0.881	0.07 0.009 0.889	0.03 0.08 0.897
		r x10 3 [g s -1 ]	0	1.537	0.592	0.239	0.099	0.046	0.031	0.023	0.025	0.031


Mariana S Gustafsson
email: mariana.s.gustafsson@liu.se

Elin Wihlborg

'It is always an individual assessment': A case study on challenges of automation of income support services

Keywords: Automatization, Income support, Manufacturing logics, Service logics, e-services

Income support schemes are key policies in an inclusive welfare state. To make them legitimate they are strictly regulated. As such they provide good prerequisites for standardization and automation, in theory. The aim of this paper is to analyze a case of municipal administration of income support, where automatization is resisted despite managements' ambitions. We focus on the case workers' interpretations of changes conducive to automatization and discuss how different service logics may explain the tensions and resistance of the frontline case workers. Our findings suggest that digitalisation and automatization challenge the balance of two logics and raise concerns of accountability in exercise of public authority; and concerns of value in terms of support towards self-sustainability and social integration of the clients 1 .

Introduction

Social services are central in Scandinavian welfare systems, supporting the most vulnerable people to get an independent and reasonable standard of living as expressed in the social service legislation [1]. These extensive schemes, managed by local governments and municipalities, are based on a universalistic welfare model that rests upon principles of equality of living conditions, economic and social security and active participation in society. These schemes are thoroughly regulated and detailed regarding what to support, when, how and whom. As such the schemes are clear and provide good prerequisites for standardization and automation of case management, at least in theory. However, by virtue of the same legislation and the Administrative Procedure Act [2, 3], the case workers are guided to be accessible, transparent, supportive and guiding the client to be independent of the income support and empowered by the social workersa dilemma of accommodating different logics is established that is enhanced by digitalization.

The effects of digitalisation, as is both claimed and demonstrated over time, for improved efficiency, impartiality and the rule of law in public administration [START_REF] Heeks | Analyzing e-government research: Perspectives, philosophies, theories, methods, and practice[END_REF], public authorities are slowly introducing digital and automated processes in their service provision and administration [START_REF] Heeks | Analyzing e-government research: Perspectives, philosophies, theories, methods, and practice[END_REF][START_REF] Bannister | Defence of Bureaucracy: Governance and Public Values in a Digital Age[END_REF]. We argue hereby that social welfare is currently under digital transformation pressures, rife with tensions, where different logics that drive value production in social services clash with the logics of standardization and manufacturing that underlie imminent automation processes.

Scandinavian public welfare services are currently subject to advanced digitalization, in a context rife with diversified population needs and demands, governed by political goals of equal access to high quality services and constrained economic and personnel resources in municipal public administrations. The political ambition is to draw the benefits from technological developments to address the new demands from society [START_REF]Communication from the Commission: A Digital Agenda for Europe[END_REF]. In this context, frontline bureaucrats, as case workers, play a key role in the advanced use of digital systems in managing and administering e-services. Their discretion in case management, now mediated through technology, in relation to legal, organizational, and individual factors like competence, experiences and personal values can explain the outcomes of the welfare schemes [START_REF] Busch | Digital discretion: A systematic literature review of ICT and street-level discretion[END_REF].

The administrative organization of public services entails both principles of standardization of processes pursing management goals (NMP) and at the same time involving individualization of decisions based on clients' needs and life situations, pursuing professional ethics and social policy priorities. ICTs and automation are expected to enable and increase the manufacturing types of service production [START_REF] Cordella | ICTs and value creation in public sector: Manufacturing logic vs service logic[END_REF].

Aim

The aim of this paper is to analyze a case of municipal administration of income support, where automatization is disputed, by focusing on the case workers' interpretations of these changes and analyze how different logics may explain the concerns to change.

Research Questions

The research questions that will be pursed for this purpose are:

1. What automatization attempts can be discerned in the case of municipal administration of income support? 2. What concerns are raised in connection with automatization in this case? 3. What logics are at work and how they affect automatization in service provision of income support?

'Digital First' principle in public administration in Sweden

In line with the European Digital Agenda, the Swedish national digital strategy is establishes the principle "digital first" [START_REF]Communication from the Commission: A Digital Agenda for Europe[END_REF][START_REF]Regeringskansliet, För ett hållbart digitaliserat Sverige -en digitaliseringsstrategi[END_REF]. It implies that the contact with public authorities should primarily happen digitally. It involves submission of records in one instance, in order to streamline the case management and facilitate decision making. The clients however meet different prospects and challenges to meet the public authority, based on their municipality geographic configuration, demographic landscape and the volume of administrative resources.

2.1

The role of municipalities in the Swedish public administration

The social services in Sweden are a crucial part of the welfare state and it is formed and managed at the cross-road of two main governance principles: universalism and local autonomy [START_REF] Trydegard | One Uniform Welfare State or a Multitude of Welfare Municipalities? The Evolution of Local Variation in Swedish Elder Care[END_REF]. The income support defined in the Swedish Social Service Act [1] has is to be delivered impartially to all inhabitants, by all municipalities. National equality is key for the implementation by municipal administrations, which are to follow clear regulations and guides for application of the legislation in practice. On the other hand, the municipalities have constitutional autonomy [11], and act upon self-government powers [3].

Social service and income support schemes: Promise of automatization

The income support scheme includes two key dimensions: a thoroughly regulated administration of records on living conditions and cost of the client and an individual coaching-support service for the client that aims towards employment and financial independence. The records including living expenses and income are collected in connection to the application to entitlement for Income support and are subsequently reported monthly. Municipalities have well developed digital registries to collect, store and administer such records. The individualized coaching services involve a systematic planning, in collaboration with other authorities -both local and national -of activities to support the client to become fit for work and gain financial independence [START_REF]Socialstyrelsen, Handläggning och dokumentation inom socialtjänsten[END_REF] .

Although implementing a heavily regulated scheme, the municipalities have large powers, due to the local autonomy, to choose and develop own case management systems. Although a certain systematics for registration of records is common for the municipalities there are no standardized processes of case management in practice. A few municipalities develop their own systems, but the usual practice is to buy IT-solutions on the market [START_REF] Jansson | En legitim (elektronisk) förvaltning? Om IT-utveckling i kommunal förvaltning[END_REF]. Such solutions, commonly built on a model developed for one municipality, are subsequently sold to other municipalities with the promise of adaptation to the municipality's needs and case management processes.

Models of automation has already started to be implemented in public administration in Sweden, with a few examples from national agencies [START_REF] Wihlborg | The Computer Says No!" -A Case Study on Automated Decision-Making in Public Authorities[END_REF]. A majority (55%) of the Swedish municipalities report offering e-services with either totally or partially automatized service management [15]. There is an abundance of studies focusing on the effects of digitalization in public sector but less on automatization of processes in social welfare services. There are some examples in human resources-processes, where software robots collect records from several different IT systems and register data rapidly and without bias [START_REF] Willcocks | Service automation robots and the future of work[END_REF]. In the Swedish municipalities we can find several recent examples. The most known model is from the social services in Trelleborg, that has been described as a success model for automation in social services: extra time and personnel resources could be allocated on coaching the clients towards reintegration on labor market [START_REF] Valcon | Process automation in Trelleborg municipality[END_REF][START_REF] Ranerup | Value positions in digitalization and automated decisionmaking in social work[END_REF]. This model is currently disseminated in 14 municipalities with support from national agencies as Vinnova and SALAR [START_REF] Scaramuzzino | Socialarbetare om automatisering i socialt arbete: En webbenkätundersökning [Social workers on automatisation of social work: A websurvey[END_REF].

In other municipalities, this model has been criticized. One of the most discussed cases is from Kungsbacka municipality, where 12 out of 16 social workers resigned in protest to the plans for automation of income support [START_REF] Persson | The Success model in Trelleborg meets resistance: "They copy[END_REF]. The protesting social workers acknowledged that digitalization may save time, but they questioned that a robot can make individual assessments of their clients' needs. Other critique involved the shift to a labor market perspective from social care, the fear for losing the professional identity under an administrative organizational change (from social care unit to a labor market unit in the municipal administration) and the lacking dialog between leadership and the social workers [START_REF] Persson | The Success model in Trelleborg meets resistance: "They copy[END_REF]. The two examples of automatization: in Trelleborg municipality and Kungsbacka municipality show that one single model of automation -when copied to other municipalities -got different response and support from the frontline case workers. Thus, it was important for us to follow closely similar implementation practices conducive to automatization changes and examine what tensions and logics guided the process.

Implementation barriers for digitalization in public administration

Research on innovation in public administration focusing e-government reforms has specifically and predominantly been concerned with barriers to adoption and advancement [START_REF] Savoldelli | Understanding the e-government paradox: Learning from literature and practice on barriers to adoption[END_REF][START_REF] Schwester | Examining the Barriers to e-Government Adoption[END_REF][START_REF] Mergel | Open innovation in the public sector: drivers and barriers for the adoption of Challenge.gov[END_REF]. But there are also approaches focusing on flexibility and agility in implementation processes [START_REF] Gong | From policy implementation to business process management: Principles for creating flexibility and agility[END_REF]. Building on these approaches we will also open for an analysis of logics and values embedded into public administration practices to search explanations of the case workers hesitations to innovate.

Barriers in implementing digital innovations in public services

Digital government barriers are predominantly studied as technical challenges, disincentivizing actions, dysfunctional organizations and ambiguous institutional structures that constrain practice, lack of-or unclear policy [START_REF] Gustafsson | Reassembling Local E-Government: A study of actors' translations of digitalisation in public administration[END_REF]. Barriers have been systematized according to different models. However, compared to the attention given to technological, organizational and structural barriers, considerable less attention has been attributed to cultural barriers [START_REF] Meijer | E-governance innovation: Barriers and strategies[END_REF]. Cultural barriers in digital government, as studied by Margetts and Dunleavy [START_REF] Margetts | Cultural barriers to e-government[END_REF], refer to a scaring image of technology in organizations, according to which minor mistakes in usage may lead to terrible consequences. Such perceptions pose hinders to implementation of technological change. In a more flexible and agile approach, Gong and Janssen [START_REF] Gong | From policy implementation to business process management: Principles for creating flexibility and agility[END_REF] identify four keys for good implementation of digital government processes: separating the process from the service, pre-planned (not event-driven) integration and orchestration of implementation, embedding knowledge and resources into the process of change.

Framing in governance of innovation has shown to play a key part in successful innovation and of government strategies to address resistance to technological change. Meijer [START_REF] Meijer | E-governance innovation: Barriers and strategies[END_REF] has found that connecting technological opportunities to the production of public value are crucial in this respect. In similar ways, Pors [START_REF] Pors | Becoming digital -passages to service in the digitized bureaucracy[END_REF] found that digitalization fundamentally changed the modes of work of frontline bureaucracy and their interaction with citizens, from providing citizen service to providing citizen support.

Through digitalization and co-production in a 'digital first' setting, citizens took over a part of the administrative tasks through digital systems which gave the frontline case workers new possibilities to guide and support the citizens, rather than solve their clients' cases. This research shows that implementation of digital innovations for services towards citizens in these practices opens for and requires new logics of service provision.

Logics of digital service provision

Digitalization of public services transform the organization of public sector [START_REF] Cordella | ICTs and value creation in public sector: Manufacturing logic vs service logic[END_REF][START_REF] Cordella | E-government and organizational change: Reappraising the role of ICT and bureaucracy in public service delivery[END_REF][START_REF] Margetts | The second wave of digital-era governance: a quasi-paradigm for government on the Web[END_REF] and challenge the Weberian model of public service production. Cordella, Paletti [START_REF] Cordella | ICTs and value creation in public sector: Manufacturing logic vs service logic[END_REF] identify two different logics of value creation: manufacturing logic and service logic.

The manufacturing logic, following industrial production and market logics, is reflected in standardization of production processes to create value. The manufacturing logic involves essentially the standardization principle, according to which the organization focuses on improving organizational set-ups and streamlining of production processes and means in order to produce a desired value. Digitalization opens even further for new ways to organize and manage NPM based service production in public sector. Such effects, argue Cordella, Paletti [START_REF] Cordella | ICTs and value creation in public sector: Manufacturing logic vs service logic[END_REF] leads to a shift in logics of production in public organizations towards service logic of value creation, involving market and civil society actors in co-production of public services. The resources available for such a process complement the in-house resources of public administrations opening the value creation process to external resources, processes, interests and capabilities. The two logics of service production and value creation are summarized as follows, in Table 1 Adapted from [START_REF] Cordella | ICTs and value creation in public sector: Manufacturing logic vs service logic[END_REF] Public values such as impartiality, fairness and equality are fundamental for all public services both logics of service production and guide the public administrations. However, within these core values there are different values underlying the two logics. The 'manufacturing logic' are more standardized and less flexible, a service logic emphasize values of individualization and flexibility. This model will guide our analysis of how and why the municipal case workers may address different assignments -controlling or coaching -in their daily working meeting with clients and the automated system.

Methods and research design for the case study

Being part of a larger project that focused on understanding of legitimate exercise of public authority in the context of automated case processing and decision making, this study was designed as a single case study of implementation practices in units that were introducing e-services and aiming at automatization. Material collection included elements of action research and abduction in terms of connection to the theory [START_REF] Alvesson | Reflexive methodology: new vistas for qualitative research[END_REF]. While working on the case we shared knowledge with the municipality. The research is based on two planning meetings, gathering researchers, unit management and municipality digitalisation strategist, where we participated and documented discussions focusing on organizational set up, the change management, implementation process, as well challenges. Observations under two demonstration workshops aiming to acquaint all the case workers with the function 'My Pages' ('Mina sidor'), and 'e-Application' ('e-Ansökan'). Five semi-structured interviews were carried with key personnel in the unit: the unit manager, the lead case worker (most experienced in the team), two case workers who were 'super-users' of the platform (most knowledgeable IT-users in the unit, who also have qualifications for testing new functions and e-services on their cases before the rest of the case workers start using them). In addition, we coordinated two knowledge meetings with the management and one workshop with the entire unit, focusing on validation and discussion of our research findings, their organizational implications and practical advice.

The model comparing the two service production logics has been used in the analysis to discern qualitatively the organizational set-up for the change that involves introduction of e-services, as well as to the underlying logics that explained the different experiences and interpretations of the different professionals in the public sector.

5

The income support in the municipality

Organizational set-up accommodating both manufacturing and service logics

The municipal organizational set-up for the Income support services is following a hierarchical structure where the manager of the unit is accountable to a chain of managers higher up in the administration of social services. The financial resources making up the budget are drawn from the municipal pool of publicly collected taxes. Such an organization, follows centralized municipal planning and by law relies on a close production cycle, thus following a manufacturing logic. The case workers are the sole professionals with mandates to exercise public authority upon income support decisions. However, in the process re-habilitation and re-integration of the client in society, the case workers must collaborate with other authorities as described below. Such a collaboration between the authorities, involves a pooling of resources across organizations, thus making the production cycle open and employing co-production practices.

Integrating e-services challenges the accommodation of the two logics

Case management of the income support in the municipality is administered through the internal IT-system, VIVA, where case workers register, follow up and handle all the cases and the pertaining records. When the client submits a paper-application for income support, a new case is opened and the records are manually introduced in VIVA.

The records on income and expenses from the application, are currently manually registered in VIVA. Besides place of residence, family members' residence and their employment situation, the records include public social insurance allowances such as unemployment, sick leave and child benefits. The new records are usually incomplete, which always requires a cross-check through the registry system s of the different authorities (Tax Authority, Social Insurance Agency, Swedish Board of Student Finance, Public Employment Service and the Unemployment Insurance Funds). Record registration and their clarification makes up the part of the services that is mostly regulated, standardized and repetitive, is clearly following a manufacturing logic. This part of the service is expected to become more effective and time saving through e-services and automatization.

Following the national digitalization policies and the municipality action plan, the unit is currently introducing the e-services 'e-Application' (e-Ansökan) and 'My Pages' (Mina sidor) for the income support scheme. This initiative was initiated in 2017 and is still under implementation. It intends to partially digitalize the application process that is currently entirely made on paper. The plan is that the very first application will still be done on paper, while the subsequent ones, from the same client, will be done online through e-Application and My Pages. The e-Application service was integrated in VIVA by e-Lab during in 2018. The ambitions are that the e-services will increase the accessibility for the client and facilitate them to submit more and correct records.

Both management and part of the case workers expected the quality of the records to improve and the process to be more effective, streamlining it towards better decisions and more coaching towards employment and social re-integration. The main risks that were foreseen by the case workers were the clients who could abuse the service and the increase in the number of cases per case worker. Consequently, in terms of improving quality of records and their registration -part of the case workers' and the management -agree that ICTs and automatization can enable time saving and effective processes. In terms of coaching and support, steered by a service-logics, both by law and by professional ethics, the image becomes more complicated.

Individual micro-assessments the basis of targeted interventions in social assistance and service logics as its core

Upon each application for income support, the case worker needs to get all relevant and correct records on income and expenses, where the latter ones always exceed the former one. Besides pursuing the calculations entitling the client for financial support, the case worker needs to make individual 'micro-assessments' on whether the expenses are eligible and legitimate to cover through the scheme. In such micro-assessments, the case worker has important discretionary power: how many jobs has the client applied for, participation in rehabilitation activities (ex. practical training, work training). Based on the principle of individually targeted interventions in social assistance, in every assessment, the case worker considers holistically the individual's records and his specific life situation: how do they act to improve their living, do they do what they must, what is reasonable to require from the person, how their children affected by the decision? These micro-assessments which underlie the authority decisions to provide income support, in combination with coaching are fundamental in steering the clients' actions towards financial independence. It implies guiding the clients in a desired direction, as a service logic to pursue rehabilitation, re-connect with family, follow doctors' prescriptions and finally apply for jobs. Value production involves meaningful communication with the client to calibrate the demands, to clarify the expectations and to plan for further activities that aim to return the client on the work market and financial independence. This part of the service production and value creation is thus guided by a service logic that builds on an interaction and communication with the individual client on the one side and case workers from other authorities on the other, in order to guide, advice and support toward self-sufficiency and independence.

The accommodation of manufacturing logics that underlies planning and organizational set-up, but also records registration in case work -with a service logic, that underlies coaching and support seems to be challenged by the prospects of automatization, as illustrated by the citation below:

We talk a lot about saving time, specifically concerning applications. We spend a lot of time to process the application, to work with papers… to go through the manual records, bills and invoices. The entire process is very time consuming, but we would like to spend more time with the people, meet them more and spend more time on coaching them to go on and get an own maintenance. Everything that can save time for us is welcome. For example, if the records are matched automatically to the open cases and we skip filling these manually, could save 1 minute per application. If you deal with 70 applications and save 1 hour that can be used on coaching the client or receive one extra visit. (Case worker 1) At the same time, concerns arise related to responsibility and legality of decisions making based on individual assessment and ambiguities arising from the delegation of exercise of authority to a non-human:

It is difficult for me to imagine that I would not sit at the computer and press the button, because of individual assessments. But say a computer shall make the decision, who is to be accountable for that decision? It should always be a human behind the decision, legally speaking… I feel worried, because all the decisions that I am delegated to, I shall be in charge and knowledgeable of. Shall a computer make decisions that were delegated to me? And if the client would like to enquire on the decision, who is he to call if it was entirely made by a computer? (Case worker 2)

Importantly, for such a management to work and for individual micro-assessments to be possible, it needs personal interaction with the client to understand the individual's needs and capability, as well as channels of trust and constructive communication that will allow coaching towards financial independence. This is a logic of service provision, where the pursued public value is the independent and socially integrated individual. This logic is contrasting the manufacturing logic of standardization, that would not allow for individual coaching, empowerment and care. It indicates that the case workers are both striving to meet standardization of assessments and control data through automated systems, and to be service minded by coaching and service.

5.4

No drastic changes in terms of case management process and time but hope on better quality of cases and decisions.

Although the automated system will imply introducing new routines in handling the cases, no drastic changes will occur in daily work, according to the interviewed case workers. The experiences of using the e-Application for 12 months, when the case workers had only seen a Beta-version of the system, are raising more questions rather than answers for the them. The following quotations illustrate the pursuit of manufacturing-oriented logic and values such as effectiveness in terms of time saving, legality and correctness of records. The case workers are concerned with ambiguities of the new technical changes in the system and their implication for the routines.

It would be very good if it became more effective, that I saved time so that I can use that time to get them out to work or on motivating them… But I am doubtful that it will do that, because I will anyway need to make the calculations and the inspection just as usual: check that we have received the application, that it is complete, send requests for complementary information. I have difficulties seeing where I can save the time. But it can be that that I don't know too much yet. For example, what about the paper receipts that need to be attached to the application? We need to see the medicine that has been purchased and the doctor visits. Shall they scan these receipts, or shall they submit them on paper?' (Case worker 2)

A similar hesitation was raised by another case worker saying:

We will do the same things that we are doing today…, but we won't need a paperapplication to inspect. Instead everything will be done on the computer. So, I don't think we will work differently with the applications. Everything will be stored on the computer. It will surely take as much time as it takes today, no more -no less.

(Case worker 1)

The manufacturing logics shows up when the case worker reflects upon the legality and correctness of the records that can be improved by the e-Application process.

An algorithm could not make the job entirely -or?

If record management through the digital platforms -is somewhat positively seen by the interviewees, with potential to increase accuracy of data and facilitate correct decisions. The part involving meaningful communication, coaching and steering cannot be done by the automated processes, according to our interviewees. It proved difficult for the case workers to see how algorithms could make individual micro-assessments, with no meaningful communication with the client and no understanding of the client's broader life situation that goes beyond the individual records from the application. The interviewees emphasized that there are many circumstances that should be considered. The demands that a case worker posed one month, were not raised the month after due to ex. negative effects on children involved, or death of family member, as illustrated by the utterance below:

We have the rules and the regulations… So to take an example with reimbursing the expenses for a bus card. The rule sets up 3 km as a minimum distance to the destination of the planned activity (f.ex. studies, work, work training). In such a case we also make individual assessments. For example, if we get a medical certificate that proves that the person cannot walk 3 km, then we can grant him the bus card anyway. So, things like that, I think I'm having trouble seeing how it would work. And this is the issue with most of our individual assessments. So, it's difficult for me to see how these can be automated, actually. (Case worker 2)

Again, the service-logic, the responsibility for pursuing the steering of individual towards independence is illustrated in the reflection below -a logic that defies automated decision making and standardization:

You shall see to the human individual that he attains a reasonable standard of living. If the person cannot reach the workplace and cannot manage it in a good way because I denied him this bus card… I think it is my responsibility to offer this prerequisite so that he can manage his work. Otherwise, maybe if I just reject it, I think maybe that person may not be able to get to work, may not manage to do his job and even his mental health may get worse. This then may lead to that he loses his income support because he didn't show up at work. (Case worker 1).

At the same time, the case worker admitted that probably some unambiguous or noncomplicated cases could be automatized, although the total exclusion of human contact seemed unreasonable. For example, such cases, that are scarce, would be when the client is not capable of returning to the labor market and no such demands are posed on him, his actual benefits, ex. partial sick leave benefits are fixed and his expenses are more or less the same every month. Consequently, correct and complete formal records is a pre-condition for making rightful assessments, but even when these are present, the more complicated cases involve almost always cooperating with other authorities. It is common that complications arise when the different authorities make different assessments in the same case. For example, when assessing the client's ability to work, the Employment agency can assess that the client as not able to work, while a doctor decides differently. The case worker's role, where the client finally turns to, is then to untangle the problem and such entanglements cannot be fixed automatically, it was explained.

Conclusions

The ambitions to make public administration more efficient by using different forms digital support systems and not at least new forms of automatization have clear implications on the legitimacy of exercise of public authority. Importantly, our case study shows that while Swedish social assistance services in Income support are managed in a legal and organizational set-up that accommodates manufacturing logics with service logics underlying social assistance regulations and professional ethics. Digitalisation and automatization challenge this balance and raises concerns of accountability in exercise of public authority; and concerns of value in terms of support towards self-sustainability and social integration. This points to the need for further studies on le Our case study has shown that the main hesitation among the professional streetlevel to towards implementation of automatization is based in their fear that it would bring encompassing manufacturing services logic. They are doubtful and hesitant since the automatization of the income-support builds on high degree of standardizations, hiding the large variation among the clients and thereby also reducing their discretion to coach and support the clients in different ways. Thus, we can see that there is a need to design and manage automatization of public administration in ways that it is seen as keeping and promoting a service logic giving space for values like individual adoption and flexibility.

Table 1 . Logics of service production and value creation Manufacturing Logic of service production and value creation Service Logic of service production and value creation

 1 :

	Planning	Centralized	Decentralized
	Production cycle	Closed	Open
	Production process	In-house, or inter-organizational	Co-production
	Resources	Exclusively internal	Combining internal with external
		Reduction variation	Openness for variation
	Contribution	Is known, defined and measurable	Is not completely known, fuzzy and only
			partially measurable
	ICT-use	For standardization, optimization	For enabling co-production
		and efficiency
	Value is created based	Impartiality, standardization, rule	Personal interaction, adoption to co-
	on	of law	production needs and individual values

carry this research, through financing of the project: "The computer says no!" -en studie om det offentligas legitimitet och medborgares tillit när e-förvaltningen växer fram. We are also grateful to our informants in the Income Support unit in the municipality who shared their perceptions and experiences in this research.