Effect of carbonization process on physiochemical properties of digestate

doi:10.16085/j.issn.1000-6613.2018-1011

Abstract

Abstract:

The digestate after the first-stage dehydration was used as the raw material in this study. Its weight loss behavior and the compositions of the pyrolysis gas products were analyzed by thermogravimetry-Fourier Transform infrared spectroscopy ( TG-FTIR). The single-factor test method was used to investigate the effects of carbonization temperature, heating rate and holding time on the yields and physiochemical properties of biochar. The results showed that the pyrolysis reactions mainly took place at the temperature range of 360－480℃. The yield and volatile content of biochar gradually decreased with the increase of pyrolysis temperature, while its ash content increased correspondingly. The highest content (18.37%) of fixed carbon in char was obtained at 700℃. The increase of heating rate had led to the increase in the contents of ash and fixed carbon in biochar, as well as result in the reduction in char yield and volatile content in biochar. In the meantime, the yield of biochar decreased gradually with the increase of holding time. The effect of holding time on the contents of ash, volatile and fixed carbon in biochar was insignificant. The calorific values of raw material and biochar were all low. The contents of heavy metals Cd and Pb in the produced biochar were lower than those indicated in the standard of "Organic/inorganic compound fertilizer "(GB18877—2009). Hg and Cr contents in the biochars were low, which was within the limits of harmful heavy metal elements in fertilizers. On the other hand, the contents of elements of Mn and Zn that are beneficial to plant growth were high. This study provides a theoretical basis for using the digestate as raw materials to produce fertilizers.

Key words: digestate, pyrolysis, carbonization process, biochar yield, heavy metal

摘要：

以一级脱水沼渣为原料，通过热重-红外联用分析其失重行为及热解气相产物的组成，采用单因素试验方法，考察炭化温度、升温速率、保温时间对沼渣炭的得率、理化性质的影响。结果表明：360～480℃区域为热解的主要阶段。随着温度的升高，炭得率、挥发分含量降低，灰分含量增加，固定碳含量在700℃最高（18.37%）；随着升温速率提高，灰分、固定碳含量提高，炭得率及挥发分含量降低；随着保温时间的延长，炭得率逐渐降低，对灰分、挥发分、固定碳影响不显著；原料及炭热值较低；重金属Cd和Pb含量低于“有机-无机复混肥料”标准限值（GB 18877—2009）；Hg和Cr含量较低，符合肥料用有害重金属元素限值标准，而有益于植物生长的元素Mn和Zn含量较高，本研究为减量化处理复杂沼渣提供了理论依据。

关键词: 脱水沼渣, 热解, 炭化工艺, 得炭率, 重金属

CLC Number:

TQ914.3

Liangcai WANG,Huanhuan MA,Jianbin ZHOU. Effect of carbonization process on physiochemical properties of digestate[J]. Chemical Industry and Engineering Progress, 2019, 38(03): 1545-1551.

王亮才,马欢欢,周建斌. 炭化工艺对脱水沼渣炭理化性质的影响[J]. 化工进展, 2019, 38(03): 1545-1551.

Figures/Tables 10

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炭化温度/℃	灰分 /%	挥发分/%	固定碳/%	N /%	C /%	H /%	S /%	O /%	热值 /kJ·kg^-1
500	71.76	16.37	11.87	0.59	18.26	0.014	0.261	9.115	4351
600	74.38	10.32	15.30	0.56	16.80	0.034	0.331	7.895	4264
700	77.02	4.61	18.37	0.57	16.15	0.037	0.289	5.934	4269
800	82.56	2.41	15.03	0.30	14.06	0.019	0.147	2.914	4175

炭化温度/℃	灰分 /%	挥发分/%	固定碳/%	N /%	C /%	H /%	S /%	O /%	热值 /kJ·kg^-1
500	71.76	16.37	11.87	0.59	18.26	0.014	0.261	9.115	4351
600	74.38	10.32	15.30	0.56	16.80	0.034	0.331	7.895	4264
700	77.02	4.61	18.37	0.57	16.15	0.037	0.289	5.934	4269
800	82.56	2.41	15.03	0.30	14.06	0.019	0.147	2.914	4175

升温速率 /℃·min^-1	灰分 /%	挥发分 /%	固定碳 /%	N /%	C /%	H /%	S /%	O /%	热值 /kJ·kg^-1
10	76.47	6.87	16.75	0.57	16.15	0.037	0.289	5.934	4267
15	76.84	6.12	17.04	0.55	16.35	0.036	0.330	6.132	4268
20	76.86	5.43	17.71	0.54	16.21	0.035	0.311	5.978	4267
25	77.02	4.61	18.37	0.52	16.30	0.033	0.288	5.914	4269

升温速率 /℃·min^-1	灰分 /%	挥发分 /%	固定碳 /%	N /%	C /%	H /%	S /%	O /%	热值 /kJ·kg^-1
10	76.47	6.87	16.75	0.57	16.15	0.037	0.289	5.934	4267
15	76.84	6.12	17.04	0.55	16.35	0.036	0.330	6.132	4268
20	76.86	5.43	17.71	0.54	16.21	0.035	0.311	5.978	4267
25	77.02	4.61	18.37	0.52	16.30	0.033	0.288	5.914	4269

保温时间/min	灰分/%	挥发分/%	固定碳/%	N /%	C /%	H /%	S /%	O /%	热值/kJ·kg^-1
30	77.02	4.61	18.37	0.57	16.15	0.037	0.289	5.934	4269
60	77.84	5.34	18.82	0.49	18.84	0.029	0.281	2.52	4623
90	77.90	3.83	18.27	0.50	20.63	0.025	0.254	0.691	4843
120	78.05	3.52	18.53	0.56	20.86	0.021	0.209	0.300	4875