Investigation on thermochemical conversion characteristics and regularity of co-hydrothermal carbonization solid fuel from sewage sludge and lignite

doi:10.11949/0438-1157.20191419

Abstract

Abstract:

The sludge and lignite are pretreated by co-hydrothermal carbonization to prepare high-quality solid fuel, which provides a feasible solution for the effective treatment of sludge and low-rank coal. This study mainly investigated the thermochemical conversion characteristics and regularity of solid phase products (hydrochars) prepared by Co-HTC of sewage sludge (SS) and lignite (LC) at different temperatures (120, 180, 240 and 300℃). Experiments included combustion, pyrolysis and char CO₂-gasification processes, and the synergistic effects in these processes were also analyzed. The results show that Co-HTC pretreatment has some significant effects on the thermal behavior of SS and LC. On the one hand, compared with the calculated value, the hydrochars after co-hydrothermal carbonization have higher yield, fuel rate, coalification degree, calorific value, etc., and they have lower ash content. On the other hand, all hydrochars have a certain synergistic effects in combustion, pyrolysis and char CO₂-gasification (promoting combustion and pyrolysis behavior, reducing gasification activity), and when the hydrothermal temperature is around 240℃, these synergistic effects are most obvious. Given that the synergistic effects of the pyrolysis and gasification processes are lower than the combustion process, co-hydrothermal carbonization products are considered to be more suitable for combustion. These findings indicate that the combination of the upgrading of Co-HTC with subsequent thermochemical processes has positive implications for the generation of energy and the utilization of organic wastes.

Key words: sewage sludge, lignite, co-hydrothermal carbonization, combustion characteristics, pyrolysis reactivity, CO₂-gasification, synergistic effect

摘要：

污泥和褐煤通过共水热碳化预处理以制备高品质固体燃料，为污泥和低阶煤的有效处理提供了一种可行方案。本研究主要考察了城市污泥（SS）和褐煤（LC）在不同温度下（120，180，240和300℃）进行共水热碳化制得的固相产物（水热炭）的热化学转化特性和规律，包括燃烧、热解和半焦CO₂气化过程，并分析了这些过程中的协同作用。结果表明，共水热碳化预处理对城市污泥和褐煤的热利用行为有显著影响。一方面，共水热碳化处理后的水热炭相对其计算值具有更高的产率、煤化程度、热值等，同时具有更低的灰分含量。另一方面，混合物水热炭在燃烧、热解和半焦CO₂气化过程均表现出一定的协同作用（促进燃烧和热解行为，降低气化活性），且水热温度在240℃附近时，这种作用最为明显。鉴于热解和气化过程的协同效果均低于燃烧过程，共水热碳化产物被认为更适合用于燃烧。这些发现表明，将共水热碳化改性提质处理与后续热化学工艺相结合，对于能源的产生和有机废弃物的利用都有一定的积极意义。

关键词: 城市污泥, 褐煤, 共水热碳化, 燃烧特性, 热解反应性, 半焦CO₂气化, 协同作用

CLC Number:

TK 6

Yanpei SONG, Xiuzheng ZHUANG, Hao ZHAN, Bin XU, Xiuli YIN, Chuangzhi WU. Investigation on thermochemical conversion characteristics and regularity of co-hydrothermal carbonization solid fuel from sewage sludge and lignite[J]. CIESC Journal, 2020, 71(5): 2320-2332.

宋艳培, 庄修政, 詹昊, 徐彬, 阴秀丽, 吴创之. 城市污泥/褐煤共水热碳化产物的热化学转化特性及规律研究[J]. 化工学报, 2020, 71(5): 2320-2332.

Figures/Tables 11

References 38

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Sample		Yield /%	Proximate analysis /%(mass, db)			Ultimate analysis /%(mass, daf)					HHV/ (MJ·kg^-1)
Sample		(mass, db)	A	VM	FC	C	H	O	N	S	HHV/ (MJ·kg^-1)
SS	SS-Raw	/	56.24	39.15	4.61	48.53	8.07	34.49	7.52	1.40	9.38
	SS-120	88.34	61.22	34.30	4.48	49.77	8.16	34.19	6.42	1.45	8.23
	SS-180	74.92	70.40	26.13	3.47	52.81	8.39	31.56	5.70	1.53	6.65
	SS-240	70.45	76.21	20.27	3.52	56.18	8.83	27.90	5.44	1.64	5.70
	SS-300	68.00	79.44	17.08	3.48	58.32	9.04	25.67	5.16	1.80	5.02
LC	LC-Raw	/	6.97	50.65	42.38	65.10	5.68	27.37	1.41	0.43	23.95
	LC-120	95.41	6.59	50.07	43.34	65.67	5.28	27.32	1.36	0.36	24.38
	LC-180	93.59	6.67	49.25	44.08	66.73	5.23	26.35	1.34	0.35	24.42
	LC-240	89.46	6.81	48.95	44.24	67.60	5.23	25.53	1.33	0.31	24.74
	LC-300	80.36	6.65	46.10	47.24	68.56	5.13	24.71	1.31	0.28	25.40
theoretical mixture	Mix-120(C)	91.88	33.91	42.18	23.91	57.72	6.72	30.76	3.89	0.91	16.31
	Mix-180(C)	84.26	38.53	37.69	23.77	59.77	6.81	28.95	3.52	0.94	15.55
	Mix-240(C)	79.95	41.51	34.61	23.88	61.89	7.03	26.72	3.38	0.98	15.22
	Mix-300(C)	74.18	43.05	31.59	25.36	63.44	7.09	25.19	3.24	1.04	15.21
mixture	Mix-120(E)	92.86	32.83	42.30	24.87	60.58	6.47	29.71	2.68	0.57	16.78
	Mix-180(E)	86.81	34.69	39.91	25.39	63.26	6.35	27.22	2.62	0.56	16.79
	Mix-240(E)	82.82	36.39	37.97	25.64	65.27	6.26	25.42	2.55	0.50	16.93
	Mix-300(E)	74.88	40.38	32.70	26.92	67.11	6.14	23.84	2.46	0.46	16.62

Sample		Yield /%	Proximate analysis /%(mass, db)			Ultimate analysis /%(mass, daf)					HHV/ (MJ·kg^-1)
Sample		(mass, db)	A	VM	FC	C	H	O	N	S	HHV/ (MJ·kg^-1)
SS	SS-Raw	/	56.24	39.15	4.61	48.53	8.07	34.49	7.52	1.40	9.38
	SS-120	88.34	61.22	34.30	4.48	49.77	8.16	34.19	6.42	1.45	8.23
	SS-180	74.92	70.40	26.13	3.47	52.81	8.39	31.56	5.70	1.53	6.65
	SS-240	70.45	76.21	20.27	3.52	56.18	8.83	27.90	5.44	1.64	5.70
	SS-300	68.00	79.44	17.08	3.48	58.32	9.04	25.67	5.16	1.80	5.02
LC	LC-Raw	/	6.97	50.65	42.38	65.10	5.68	27.37	1.41	0.43	23.95
	LC-120	95.41	6.59	50.07	43.34	65.67	5.28	27.32	1.36	0.36	24.38
	LC-180	93.59	6.67	49.25	44.08	66.73	5.23	26.35	1.34	0.35	24.42
	LC-240	89.46	6.81	48.95	44.24	67.60	5.23	25.53	1.33	0.31	24.74
	LC-300	80.36	6.65	46.10	47.24	68.56	5.13	24.71	1.31	0.28	25.40
theoretical mixture	Mix-120(C)	91.88	33.91	42.18	23.91	57.72	6.72	30.76	3.89	0.91	16.31
	Mix-180(C)	84.26	38.53	37.69	23.77	59.77	6.81	28.95	3.52	0.94	15.55
	Mix-240(C)	79.95	41.51	34.61	23.88	61.89	7.03	26.72	3.38	0.98	15.22
	Mix-300(C)	74.18	43.05	31.59	25.36	63.44	7.09	25.19	3.24	1.04	15.21
mixture	Mix-120(E)	92.86	32.83	42.30	24.87	60.58	6.47	29.71	2.68	0.57	16.78
	Mix-180(E)	86.81	34.69	39.91	25.39	63.26	6.35	27.22	2.62	0.56	16.79
	Mix-240(E)	82.82	36.39	37.97	25.64	65.27	6.26	25.42	2.55	0.50	16.93
	Mix-300(E)	74.88	40.38	32.70	26.92	67.11	6.14	23.84	2.46	0.46	16.62

Sample	Residue / % (mass)	Characteristic temperatures /℃			t_b / min	(dw/dt)_max / (%(mass)·min^-1)	(dw/dt)_mean / (%(mass)·min^-1)	S×10⁸
Sample	Residue / % (mass)	T_i	T_m	T_b	t_b / min	(dw/dt)_max / (%(mass)·min^-1)	(dw/dt)_mean / (%(mass)·min^-1)	S×10⁸
SS-Raw	57.95	215.43	318.46	708.24	49.28	1.80	0.48	2.65
SS-120	63.57	219.87	315.88	712.55	49.27	1.64	0.42	1.99
SS-180	70.61	223.59	318.47	715.35	49.18	1.57	0.34	1.48
SS-240	77.66	247.57	383.97	717.72	47.02	0.91	0.26	0.53
SS-300	78.83	262.92	389.35	730.65	46.77	0.95	0.24	0.46
LC-Raw	8.58	322.06	378.80	505.06	18.30	10.54	1.05	21.14
LC-120	3.82	325.18	373.62	505.70	18.05	11.09	1.11	22.93
LC-180	10.18	330.56	371.04	504.84	17.43	11.66	1.03	21.82
LC-240	9.36	335.79	363.28	502.90	16.71	14.12	1.04	25.94
LC-300	7.48	337.32	363.07	481.35	14.40	11.17	1.06	21.69
Mix-120(C)	34.63	312.78	368.37	520.88	20.81	6.42	0.75	9.47
Mix-180(C)	40.41	314.02	375.96	517.34	20.33	6.18	0.68	8.30
Mix-240(C)	43.47	319.56	363.42	510.33	19.08	7.54	0.65	9.40
Mix-300(C)	43.47	323.33	365.79	507.10	18.38	5.84	0.65	7.04
Mix-120(E)	30.44	312.78	370.74	520.97	20.82	6.09	0.80	9.55
Mix-180(E)	34.52	314.02	378.54	517.91	20.39	6.74	0.75	9.93
Mix-240(E)	33.84	324.17	378.93	514.65	19.05	7.74	0.76	10.88
Mix-300(E)	38.03	348.63	397.25	510.48	16.19	7.82	0.71	8.98

Sample	Residue / % (mass)	Characteristic temperatures /℃			t_b / min	(dw/dt)_max / (%(mass)·min^-1)	(dw/dt)_mean / (%(mass)·min^-1)	S×10⁸
Sample	Residue / % (mass)	T_i	T_m	T_b	t_b / min	(dw/dt)_max / (%(mass)·min^-1)	(dw/dt)_mean / (%(mass)·min^-1)	S×10⁸
SS-Raw	57.95	215.43	318.46	708.24	49.28	1.80	0.48	2.65
SS-120	63.57	219.87	315.88	712.55	49.27	1.64	0.42	1.99
SS-180	70.61	223.59	318.47	715.35	49.18	1.57	0.34	1.48
SS-240	77.66	247.57	383.97	717.72	47.02	0.91	0.26	0.53
SS-300	78.83	262.92	389.35	730.65	46.77	0.95	0.24	0.46
LC-Raw	8.58	322.06	378.80	505.06	18.30	10.54	1.05	21.14
LC-120	3.82	325.18	373.62	505.70	18.05	11.09	1.11	22.93
LC-180	10.18	330.56	371.04	504.84	17.43	11.66	1.03	21.82
LC-240	9.36	335.79	363.28	502.90	16.71	14.12	1.04	25.94
LC-300	7.48	337.32	363.07	481.35	14.40	11.17	1.06	21.69
Mix-120(C)	34.63	312.78	368.37	520.88	20.81	6.42	0.75	9.47
Mix-180(C)	40.41	314.02	375.96	517.34	20.33	6.18	0.68	8.30
Mix-240(C)	43.47	319.56	363.42	510.33	19.08	7.54	0.65	9.40
Mix-300(C)	43.47	323.33	365.79	507.10	18.38	5.84	0.65	7.04
Mix-120(E)	30.44	312.78	370.74	520.97	20.82	6.09	0.80	9.55
Mix-180(E)	34.52	314.02	378.54	517.91	20.39	6.74	0.75	9.93
Mix-240(E)	33.84	324.17	378.93	514.65	19.05	7.74	0.76	10.88
Mix-300(E)	38.03	348.63	397.25	510.48	16.19	7.82	0.71	8.98

Sample	Residue/ %(mass)	Characteristic temperatures /℃			t_b / min	(dw/dt)_max / (% (mass)·min^-1)	(dw/dt)_mean / (% (mass)·min^-1)	ΔT_1/2 / ℃	D×10⁷
Sample	Residue/ %(mass)	T_i	T_m	T_b	t_b / min	(dw/dt)_max / (% (mass)·min^-1)	(dw/dt)_mean / (% (mass)·min^-1)	ΔT_1/2 / ℃	D×10⁷
SS-Raw	56.35	216.83	280.48	1086.06	86.92	1.54	0.41	198.74	22.69
SS-120	58.95	234.46	331.94	1088.34	85.39	1.49	0.38	168.83	17.86
SS-180	67.89	246.66	345.37	1089.35	84.27	1.01	0.30	228.14	5.01
SS-240	73.90	253.98	454.12	1100.00	84.60	0.65	0.24	211.66	1.70
SS-300	76.74	283.81	456.65	1100.00	81.62	0.61	0.22	152.34	1.56
LC-Raw	48.66	283.81	421.67	946.89	66.31	1.59	0.48	191.89	17.06
LC-120	47.96	293.57	417.11	921.55	62.80	1.62	0.49	186.31	17.97
LC-180	49.23	296.01	423.95	919.26	62.33	1.54	0.47	184.79	16.00
LC-240	50.72	300.89	431.05	916.98	61.61	1.59	0.46	179.72	15.48
LC-300	54.18	315.53	440.18	914.70	59.92	1.45	0.43	188.35	10.88
Mix-120(C)	53.54	239.34	422.47	1085.81	84.65	1.19	0.43	253.42	9.37
Mix-180(C)	59.51	258.58	430.97	1089.36	83.08	1.08	0.38	223.77	6.64
Mix-240(C)	61.45	283.54	433.25	1100.00	81.65	1.09	0.36	179.17	6.88
Mix-300(C)	64.98	302.77	444.91	1100.00	79.72	1.03	0.33	152.36	5.75
Mix-120(E)	55.37	244.22	424.89	1076.87	83.27	1.16	0.42	261.78	7.95
Mix-180(E)	59.16	268.62	433.25	1080.99	81.24	1.18	0.38	210.85	7.50
Mix-240(E)	60.29	288.42	437.81	1085.81	79.74	1.25	0.37	167.77	8.70
Mix-300(E)	63.55	310.65	448.45	1090.37	77.97	1.15	0.34	141.15	7.26