Optimum design and performance analysis of waste heat recovery system for biomass fermentation

doi:10.11949/0438-1157.20230641

Abstract

Abstract:

In order to solve the problem that the waste heat generated by biomass aerobic fermentation is difficult to be effectively recovered, with corn straw as the main raw material and using heat exchange method, a 100 L scale fermentation device and heat recovery system were built to recover the apparent heat and latent heat in the compost steam. The electric heating method is used to simulate aerobic fermentation heat production. The waste heat recovery process was optimized from the aspects of fluid flow, equipment insulation, water storage and heat transfer area. The heat production and heat recovery effect of the optimized system were tested. The results indicate that fluid flow rate, water tank insulation, and storage capacity have a significant impact on the heat recovery performance of the system. In the simulated heat production mode, the tank temperature can rise from 17℃ to more than 40℃. Finally, through the intermittent heat recovery method, the balanced heat recovery efficiency of the system reaches more than 57%, and the average heat recovery power reaches more than 274 kJ/h, realizing the efficient recovery of fermentation waste heat.

Key words: bioenergy, corn straw, aerobic, fermentation, heat transfer, waste heat recovery, heat exchanger

摘要：

为了解决生物质好氧发酵热能难以有效回收的问题，以玉米秸秆为主要原料，采用热交换法，搭建了100 L规模发酵装置和热回收系统，用于回收堆肥蒸汽中的显热和潜热。利用电加热方式模拟好氧发酵产热，从流体流量、设备保温、蓄水量和换热面积多个方面对余热回收工艺进行优化设计，并测试了优化后系统的产热和热回收效果。结果表明，流体流量、水箱保温和蓄水量对系统热回收性能影响较大。在模拟产热方式下，水箱温度能够从17℃升至40℃以上。最终，采用间歇性热回收方式，系统平衡热回收效率达到57%以上，平均热回收功率达到274 kJ/h以上，实现了发酵余热的高效回收。

关键词: 生物能源, 玉米秸秆, 需氧, 发酵, 传热, 余热回收, 换热器

CLC Number:

S 216.2

Wei HE, Yongna CAO, Hongru SHANG, Yinxue LI, Chao GUO, Yanling YU. Optimum design and performance analysis of waste heat recovery system for biomass fermentation[J]. CIESC Journal, 2023, 74(10): 4302-4310.

贺巍, 曹永娜, 尚宏儒, 李崯雪, 郭超, 于艳玲. 生物质发酵余热回收系统优化设计与性能分析[J]. 化工学报, 2023, 74(10): 4302-4310.

Figures/Tables 10

Fig.1 Schematic diagram of the waste heat recovery device for aerobic fermentation1—insulation layer; 2—fermentation heap; 3—porous vent pipe; 4—porous clapboard; 5—wastewater layer; 6—leachate collector; 7—fermenter; 8—water pipe; 9—porous suction pipe; 10—intake pipe; 11—pipeline air pump; 12—plate heat exchanger; 13—condensate collector; 14—pump; 15—heat storage tank; 16—air pump; 17—outlet pipe; 18—electric heating belt

Table 1 Initial thermal insulation design of the heat recovery system

部位	保温材料	热阻/(m²·℃/W)
吸气管道和水管	橡塑管套	0.70
出气管道	铝箔气泡隔热膜	0.11
换热器	铝箔气泡隔热膜	0.32
水箱	铝箔气泡隔热膜	0.21
发酵罐	壁、底：橡塑板；顶：高密度泡沫板	壁：1.77；底：0.88 顶：1.22

Fig.2 Effect of heating tape length on material temperature and heat recovery efficiency

Fig.3 Effect of fluid flow on the equilibrium temperature and heat recovery efficiency of the water tank

Table 2 Statistics and calculation results of heat recovery parameters under different thermal resistance

组别	R₁/(m²·℃/W)	R₂/(m²·℃/W)	t₁/min	T_s/℃	$E 0 0 - t 1 ¯$ /W	$E 1 0 - t 1 ¯$ /W	$η t 1$ /%
1	0.32	0.21	170±8	36.6±0.3	71.2±3.2	31.5±0.3	44.2±1.5
2	0.58	0.21	180±5	38.3±0.2	82.3±4.0	33.3±0.2	40.5±1.1
3	1.06	0.21	186±5	38.8±0.4	77.5±2.8	32.2±0.3	41.5±1.7
4	0.58	0.06	165±3	32.0±0.6	106.2±2.5	24.7±0.5	23.3±0.1
5	0.58	0.46	190±5	40.1±0.3	95.3±1.9	38.5±0.3	40.4±0.5

Table 2 Statistics and calculation results of heat recovery parameters under different thermal resistance

组别	R₁/(m²·℃/W)	R₂/(m²·℃/W)	t₁/min	T_s/℃	$E 0 0 - t 1 ¯$ /W	$E 1 0 - t 1 ¯$ /W	$η t 1$ /%
1	0.32	0.21	170±8	36.6±0.3	71.2±3.2	31.5±0.3	44.2±1.5
2	0.58	0.21	180±5	38.3±0.2	82.3±4.0	33.3±0.2	40.5±1.1
3	1.06	0.21	186±5	38.8±0.4	77.5±2.8	32.2±0.3	41.5±1.7
4	0.58	0.06	165±3	32.0±0.6	106.2±2.5	24.7±0.5	23.3±0.1
5	0.58	0.46	190±5	40.1±0.3	95.3±1.9	38.5±0.3	40.4±0.5

Fig.4 Quantitative cooling test under different thermal resistance conditions of water tank

Table 3 Statistics and calculation results of heat recovery parameters under different water storage capacity and heat exchange area

组别	m₁/kg	S/m²	t₁/min	T_s/℃	$E 0 0 - t 1 ¯$ /W	$E 1 0 - t 1 ¯$ /W	$η t 1$ /%
5	4.5	1.44	190±5	40.1±0.3	95.3±1.9	38.5±0.3	40.4±0.5
6	7.5	1.44	240±5	33.7±0.2	123.6±2.6	31.6±0.2	25.6±0.4
7	10.5	1.44	280±5	31.6±0.5	139.2±3.2	32.3±0.5	23.2±0.2
8	4.5	2.16	140±8	38.1±0.9	93.9±3.1	44.7±1.1	47.6±0.4

Table 3 Statistics and calculation results of heat recovery parameters under different water storage capacity and heat exchange area

组别	m₁/kg	S/m²	t₁/min	T_s/℃	$E 0 0 - t 1 ¯$ /W	$E 1 0 - t 1 ¯$ /W	$η t 1$ /%
5	4.5	1.44	190±5	40.1±0.3	95.3±1.9	38.5±0.3	40.4±0.5
6	7.5	1.44	240±5	33.7±0.2	123.6±2.6	31.6±0.2	25.6±0.4
7	10.5	1.44	280±5	31.6±0.5	139.2±3.2	32.3±0.5	23.2±0.2
8	4.5	2.16	140±8	38.1±0.9	93.9±3.1	44.7±1.1	47.6±0.4

Fig.5 Temperature change of 100 L aerobic fermentation

Fig.6 The change of the experimental temperature and heat recovery efficiency with time

Table 4 Comparison of system heat recovery performance under different heat production-heat recovery modes

产热方式	热回收方式	热流体进口温度/℃	热流体进口湿度/%	$E 0 0 - t 1 ¯$ /W	$E 1 0 - t 1 ¯$ /W	$η t 1$ /%
电加热模拟	连续性	52降至48	100降至77	93.9±3.1	44.7±1.1	47.6±0.4
电加热模拟	间歇性	52降至50	100降至90	120.4±4.3	79.9±3.2	66.4±0.3
好氧发酵	间歇性	53降至45	100	133.2±3.4	77.0±0.9	57.8±0.8

Table 4 Comparison of system heat recovery performance under different heat production-heat recovery modes

产热方式	热回收方式	热流体进口温度/℃	热流体进口湿度/%	$E 0 0 - t 1 ¯$ /W	$E 1 0 - t 1 ¯$ /W	$η t 1$ /%
电加热模拟	连续性	52降至48	100降至77	93.9±3.1	44.7±1.1	47.6±0.4
电加热模拟	间歇性	52降至50	100降至90	120.4±4.3	79.9±3.2	66.4±0.3
好氧发酵	间歇性	53降至45	100	133.2±3.4	77.0±0.9	57.8±0.8

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