Upgas università Tor Vergata

25 Maggio 2012 – TERRAFUTURA- Firenze - Italy
Processi innovativi per l’upgrading del biogas – Innovative processes for biogas upgrading
1
UPGAS-LOWCO2
LIFE08/ENV/IT/000429
The regeneration step: results of the tests carried out in
the pilot-scale plant
R. Baciocchi, G. Costa and D. Zingaretti

2
LIQUID/SOLID SEPARATION (FILTRATION)
Based on the results
of lab-scale
regeneration
experiments
Layout of the AwR process

3
LIQUID/SOLID SEPARATION
(VACUUM FILTRATION)
Selected for
the pilot-scale regeneration
experiments
Layout of the AwR process

Pilot-scale regeneration reactor
4
Washing and
regeneration reactor
(V= 42 l)
Filtering system
( =14 m)
Vacuum filtration
pump
Liquid
collection tank
(V= 50 l)

Pilot-scale regeneration tests
5
Objectives
 Confirm the proof of concept of the proposed process at pilot-scale
(i.e. in order to treat 8-10 l of spent absorption solution)
 Evaluate the effects of the composition of the spent absorption
solution on the efficiency of the alkaline regeneration process
 Assess the feasibility of decreasing the amount of processing water

6
Types of tests carried out
 Preliminary tests to verify the functionality of all equipment
 Tests with spent absorption solutions with the same compositions as
those adopted in the lab-scale tests
 Tests with spent solution samples at different initial concentrations
 Tests with spent solution samples produced with regenerated solutions
 Tests using second washing water for the pre-treatment washing step
 Regeneration tests with unwashed APC residues

7
Residues
 Freshly sampled APC residues from a hospital waste incineration plant
Main Composition:
2 º
NaCl
CaOHCl
Ca(OH)2
CaCO3
5 15 25 35 45 55
Very similar to
that of the
residues used in
the lab-scale
experiments

5 15 25 35 45 55
Residues
Main Composition after washing (lab-scale process with L/S = 5 l/kg)
8
2 º
Ca(OH)2
CaCO3
NaCl
CaOHCl
Ca(OH)2 =55% wt.
Weight loss after
washing: 43%

0
2
4
6
8
10
12
14
0 0,5 1 1,5 2 2,5 3 3,5 4
pH
Conc. (eq/l)
Absorption
Solution
(NaOH 2.8 eq/l)
spent
absorption
solution
9
Spent solutions
 Solutions obtained from
NaOH or KOH absorption
column tests
 Tested concentrations:
2.35-3.8 eq/l
NaOH
Na2CO3

10
Experimental procedure -Washing pretreatment
 The amounts of residues to use in each are calculated based on:
 the volume (≈8 l) and composition of the spent solution
 the composition of the washed residues [55% Ca(OH)2]
 the weight loss expected after washing [43-45%]
 the ratio between Ca(OH)2 and Na2CO3 or K2CO3 equivalents: R=1.2
i.e. the optimal ratio determined in the lab-scale tests
2.55 - 4.55 kg of APC residues
 The amount of water to use in each test is calculated based on the
amount of APC residues applying a L/S = 5 l/kg
12.8 - 22.7 l of deionized water

Experimental procedure -Washing pre-treatment
 The valve at the bottom of the reactor is closed and the required
amounts of APC residues and of distilled water are weighed and fed
into the reactor. Water
11
Residues

 The mixer is activated and after 15 minutes the vacuum pump is
turned on and connected to the liquid collection tank and the valve at
the bottom of the reactor is opened.
After filtration
12
Before filtration

 The solid material (washed residues) remains in the reactor while the
processing water is collected in the tank and analyzed (Cl- conc).
13
Contact time = 15 min.
Filtration time = 1-3 h

Experimental procedure –Regeneration process
 The spent solution is poured into the heated reactor and mixed with
the residues for a contact time sufficient to reach the desired
temperature (50-55 ºC), then the slurry solution is filtered and
analyzed (main composition and Cl- conc.) while the solid product
remains in the reactor.
14
Contact time = 1.3- 2 h
Filtration time = 0.3-1.3 h

Experimental procedure -Final washing treatment
 The amount of water to add is calculated to achieve a total L/S of 5
l/kg based on the amount of solid material in the reactor and on its
humidity. After 15 minutes of mixing the solution is filtered and
analyzed (Cl- concentration). The solid product is extracted from the
reactor and analyzed (humidity, calcite content, etc).
15
Contact time = 15 min
Filtration time = 0.5-2 h

Results - Washing pre-treatment
 Results were comparable with those of the lab-scale tests, with
measured weight losses between 30 and 45% wt.
Solid product mainly made up by Ca(OH)2 with a humidity of 42-54 %
Liquid by-product with a high concentration of Cl- (44-57 g/l)
16

0
2
4
6
8
10
12
14
0 0,5 1 1,5 2 2,5
pH
Conc. (eq/l)
spent
absorption
solution
regenerated
solution
Results – Regeneration process: solution composition
 Comparison with results of lab-scale tests: K2CO3 2.35 eq/l
17
KOH
K2CO3
Pilot-scale regeneration yield:
1.50 eq/l KOH
chemical reaction = 90%
Lab-scale regeneration yield:
1.71 eq/l KOH
chemical reaction = [OH-]reg/total conc.

0
2
4
6
8
10
12
14
0 0,5 1 1,5 2 2,5 3 3,5
pH
Conc. (eq/l)
Spent
Absorption
Solution
Regenerated
solution
Results – Regeneration process: solid composition
 Comparison with results of lab-scale tests: Na2CO3 3.2 eq/l
18
NaOH
Na2CO3
Pilot-scale regeneration yield:
2.07 eq/l NaOH
Lab-scale regeneration yield:
2.16 eq/l NaOH
chemical reaction = [OH-]reg/total conc.

Results – Regeneration process: solid product
19
 44-51 % humidity
 Mainly made up by CaCO3 (55-75%)
 CO2 storage: 200-330 gCO2/ kg washed residues
Results – Final washing treatment
 Solid product mostly CaCO3 (76-85%) with 50-55 % humidity
 Liquid by-product lower concentration of Cl- (2.2-4.4 g/l)

Results – Regeneration process: alkali conversion
Effects of the composition of the solution on the yield of the reaction
20
0
10
20
30
40
50
60
70
80
90
100
2,35 2,80 3,80
%
K2CO3 spent sol. (eq/l)
KOH
η
chemreac
η
theor
η
tot
chem reac = [OH-]reg/total conc.
theor = [OH-]reg/[CO3
2-]dil
tot = (Vreg*[OH-]reg)/ (Vsp*[CO3
2-]sp)

Effects of the composition of the solution on the yield of the reaction
21
2-]dil
2-]sp)
0
10
20
30
40
50
60
70
80
90
100
110
2,80 3,20 3,80
%
Na2CO3 spent sol. (eq/l)
NaOH
η
chemreac
η
theor
η
tot

Effects of treating spent solution samples produced from regenerated
solutions and of using final washing water for the pre-treatment step
22
2-]dil
2-]sp)
0
10
20
30
40
50
60
70
80
90
100
3,80 3.8 REG
%
KOH
η
chemreac
η
theor
η
tot

Effects of treating spent solution samples produced from regenerated
solutions and of using final washing water for the pre-treatment step
23
0
10
20
30
40
50
60
70
80
90
100
3,80 3.8 REG
%
Na2CO3 spent sol. (eq/l)
NaOH
η
chemreac
η
theor
η
tot
2-]dil
2-]sp)

Effects of using untreated APC residues for the regeneration reaction
24
2-]sp)
0
10
20
30
40
50
60
70
80
90
100
2.35 no wash 2,35
%
KOH
η
chemreac
η
theor
η
tot
2-]dil

Conclusions
 The results of the pilot-scale tests were quite similar to those
obtained in the lab
 Comparable results were achieved treating K2CO3 or Na2CO3 at
the same concentrations; from 2.8 to 3.8 eq/l the total alkali
conversion yield decreased by 10%
 Optimization: the use of 2nd treatment water for the 1st washing
step appears to be feasible
 Still underway: leaching tests on the solid product to verify if it
abides to non hazardous waste landfilling criteria
25

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