dry anaerobic digestion of municipal solid waste and digestate ...

(vertical height to deliver digestate to the reactor) for the real scale reactor is just 3 times
that of pilot reactor as given in Table B-6. But, to meet the high delivery (L/min) due to
huge size of real plant, much higher size (not just 3 times like head) of pump should be
used.
Calculations for selecting the size of pump
As the same operating conditions and feed composition will be replicated, almost the same
viscosity of the reactor material will achieve in real scale reactor. Also the practical flow
rate of real scale pump can be calculated from pilot observation as follows:
The practical flow rate of pilot pump (200 L/min) = 25 L/min
If we select a pump size of 1450 L/min for the proposed real-scale reactor,
Its practical flow rate will be: = 25/200 x 1450 = 181 L/min
Time taken to recirculate whole reactor material for 1 time
= 47000 (L)/181 (L/min)
= 260 min
Recirculation time required to achieve the recirculation rate of 2.5 Ldig/Lreactor vol./d
= 2.5 x 260 min = 650 min
Recirculation frequency: 4 times/d (in every 6 h) = 650/4 = 160 min ≈ 3 h
Table B-6 Comparison of Pump System Between Pilot and Real Reactor
Detail Pilot-scale plant Real proposed plant
Size (m 3 ) 0.7 (0.6 m dia x 2.4m height) 62.5 (3 m dia x 2.4m height)
Pump head (m) 1.7 5
Pump size (L/min) 200 1450
Observed flow rate
(L/min)
25 180
Time for 1 cycle of 22 260
recirculation (min)
Full Model Number AE1N-200 AE1N-1450
Company Allweiler Allweiler
The pump (size 1450 L/min) needs to run for 3 hours in every 6 hours to achieve the
required recirculation rate (or recirculation every alternate hour i.e. 1h on and 1h off).
Thus, this is the minimum pump size (1450 L/min) for the proposed reactor (working vol.
47 m 3 ). Because if pump size smaller than this is used, it needs to be turned-on longer time
than turned-off, which is not good. However, if we want to reduce turned-on time than
turned-off time, we need to select a pump size bigger than size 1450 L/min.
This pump size (1450) will also allow p umping of 3 times grain size and 2 times fiber
length of the material as compared to pump size 200.
8. Calculation of GHG emission reduction
Landfill methane production = 140 L/kg waste
(Bogner and Spokas, 1993)
Total methane emission, if the community landfills all the waste,
= 2000 kg waste /d 140 *L CH4/kg waste = 280000 L CH4 = 280 m 3 CH4/d
120