Effects of steam pretreatment and co-production with ethanol on the energy efficiency and process economics of combined biogas, heat and electricity production from industrial hemp

Table 3 Thermal and electrical data and energy flows of products in the various scenarios, expressed in MW

	AD	AD-R	SP-AD	SP-AD-R	Et-AD	Et-AD+
Heat duty without HI	12.4	10.8	30.3	31.1	73.1	70.0
Heat duty after HI	8.9	6.6	18.4	18.4	21.6	21.3
23 bar steam injected to SP	-	-	13.7	13.7	13.7	13.7
4 bar steam injected to SP	-	-	4.7	4.7	4.7	4.7
4 bar steam, indirect heating	4.7	5.6	-	-	3.2	2.9
90°C hot water	4.2	1.0	-	-	-	-
District heat produced¹	52.2	56.9	39.9	40.7	22.9	17.9
From FGC	21.2	22.3	16.3	16.6	12.3	9.3
From the process²	-	-	11.0	11.0	7.0	7.0
From steam cycle	35.2	35.6	12.6	13.2	3.6	1.6
Electricity generated	16.2	16.6	9.3	9.6	6.5	5.5
Electricity sold(+)/purchased(-)	10.9	10.5	4.4	4.2	-1.2	0.3
Biogas (based on LHV)	53.1	63.6	65.9	69.8	50.1	50.1
Ethanol (based on LHV)	-	-	-	-	34.1	34.1

A summary of the scenarios is given in Figure 3. The energy flow of the feedstock is 155.2 MW.
HI: heat integration, SP: steam pretreatment, FGC: flue gas condensation, LHV: lower heating value.
¹ Reduced by the duty required to heat water to 90°C for heating the process. This is the maximum capacity: the average annual capacity can be calculated by applying a factor of 0.56, which corresponds to the following assumptions: heat is delivered to the district heating system during a period of time equivalent to 4,500 hours of the maximum annual capacity. Cooling water is used during the remaining 3,500 hours to remove the heat [23].
² Excluding combined heat and power production.

ISSN: 2731-3654