Pyrolysis and combustion characteristics and kinetics of torrefied traditional Chinese medicine waste

doi:10.11949/0438-1157.20190234

Abstract

Abstract:

After the torrefied traditional Chinese medicine waste (TCMW) is baked, it is a solid fuel with potential application. However, little is known about the thermal decomposition of torrefied TCMW. In this study, the effects of torrefaction on the pyrolysis and combustion characteristics of torrefied TCMW were investigated and the kinetic parameters were evaluated. The indexes of combustible, burnout characteristic and integrated combustion performance were also evaluated. It was found that the pyrolysis of torrefied TCMW can be divided into two distinct stages, which is governed by two different reaction mechanisms. The pyrolysis of torrefied TCMW was mainly concentrated between 250—500℃ with mass loss of 57%—65%. The two DTG peaks of the torrefied TCMW are superimposed by four peaks: 265.8℃, 318℃, 364.2℃ and 412.3℃. The first three peaks were due to the thermal decomposition of hemicellulose, cellulose and lignin, respectively. The decomposition of lignin and the carbonization of solid residues gave rise to the peak at 412.3℃. The apparent activation energy of the first stage is 76.1—94.0 kJ/mol, while that is 26.8—38.8 kJ/mol for the second stage. The torrefied TCMW was easy to ignite and burnout. The ignition temperature of torrefied TCMW is in the range of 280.3—294.8℃. In general, the torrefied TCMW in 10% O₂ shows the best combustion performance. The combustion of torrefied TCMW can be divided into three stages. The first stage is mainly due to the release and combust of volatiles with the activation energy of 80.5—97.3 kJ/mol. However, the TCMW under CO₂ and 10% O₂ torrefaction has higher activation energy (99—97 kJ/mol). The second stage is attributed to the combustion of volatiles and residue char with the activation energy of 18.3—28.5 kJ/mol. The main reaction of the third stage reaction is the combustion of the char, and the activation energy is 41.8—50.6 kJ/mol. The results of this paper are helpful to understand the pyrolysis and combustion of torrefied TCMW under different conditions and develop an effective utilization process.

Key words: torrefied traditional Chinese medicine waste, waste treatment, pyrolysis, combustion characteristic, kinetics

摘要：

中药废渣经过烘焙后是一种具有应用潜力的固体燃料。采用热重分析仪对烘焙中药渣的热解及燃烧特性进行了研究，利用Kissinger-Akahira-Sunose (KAS)法及Coats-Redfern法对热解及燃烧的动力学进行求解，评估了烘焙中药渣的燃烧特性。研究发现烘焙中药渣的热分解分为2个阶段，第一阶段的活化能为76.1～94.0 kJ/mol，第二阶段的活化能为26.8～38.8 kJ/mol。烘焙中药渣的燃烧分为3段反应过程，第一阶段主要是挥发分的析出及燃烧，活化能为80.5～97.3 kJ/mol；第二阶段属于挥发分及部分焦炭的燃烧，活化能为18.3～28.5 kJ/mol；第三阶段的主要反应为残余焦炭的燃烧，活化能为41.8～50.6 kJ/mol。不同烘焙条件下制得的中药渣都较易着火燃烧，着火温度在280.3～294.8℃。经O₂烘焙的中药渣前期可燃性以及综合燃烧特性最好，最易燃尽，表明燃烧烟气烘焙中药渣是可行的。

关键词: 烘焙中药渣, 废物处理, 热解, 燃烧特性, 动力学

CLC Number:

TK 16

Shanzhi XIN, Fang HUANG, Xiaoye LIU, Qingli XU, Tie MI. Pyrolysis and combustion characteristics and kinetics of torrefied traditional Chinese medicine waste[J]. CIESC Journal, 2019, 70(8): 3142-3150.

辛善志, 黄芳, 刘晓烨, 许庆利, 米铁. 烘焙中药渣的热解与燃烧特性及其动力学分析[J]. 化工学报, 2019, 70(8): 3142-3150.

Figures/Tables 10

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样品	T _i/℃	T _h/℃	(dw/dt)_max /(%/min)		(dw/dt)_mean/ (%/min)	C _r×10⁴/ (%/(℃²·min))	C _b ×10³/ (%/(℃·min))	S×10⁷/ (%/(℃³·min²))
样品	T _i/℃	T _h/℃	第一失重峰	第二失重峰	(dw/dt)_mean/ (%/min)	C _r×10⁴/ (%/(℃²·min))	C _b ×10³/ (%/(℃·min))	S×10⁷/ (%/(℃³·min²))
230N	280.3	533.4	9.03	2.97	3.24	1.2	3.74	7.29
260N	284.4	536.8	9.13	3.05	3.29	1.13	3.62	7.13
290N	294.8	541	9.5	4.14	3.44	1.09	2.86	6.95
260CO₂	281.8	538.9	9.59	3.21	3.26	0.96	3.11	5.78
260O₂	282.9	539.2	9.47	3.43	3.33	1.18	3.71	7.31

样品	T _i/℃	T _h/℃	(dw/dt)_max /(%/min)		(dw/dt)_mean/ (%/min)	C _r×10⁴/ (%/(℃²·min))	C _b ×10³/ (%/(℃·min))	S×10⁷/ (%/(℃³·min²))
样品	T _i/℃	T _h/℃	第一失重峰	第二失重峰	(dw/dt)_mean/ (%/min)	C _r×10⁴/ (%/(℃²·min))	C _b ×10³/ (%/(℃·min))	S×10⁷/ (%/(℃³·min²))
230N	280.3	533.4	9.03	2.97	3.24	1.2	3.74	7.29
260N	284.4	536.8	9.13	3.05	3.29	1.13	3.62	7.13
290N	294.8	541	9.5	4.14	3.44	1.09	2.86	6.95
260CO₂	281.8	538.9	9.59	3.21	3.26	0.96	3.11	5.78
260O₂	282.9	539.2	9.47	3.43	3.33	1.18	3.71	7.31

样品	温度/℃	失重量/%(mass)	反应级数n	活化能E/(kJ/mol)	指前因子A/min^-1	拟合度r
230N	265—392	52.62	2	76.07	7.75 × 10⁵	0.997
230N	392—528	11.11	2	38.75	4.62 × 10²	0.998
260N	279—386	48.42	2	82.76	2.52 × 10⁶	0.999
260N	386—612	14.91	2	26.96	31.4	0.997
290N	296—390	41.03	2	94.02	1.68 × 10⁷	0.999
290N	390—656	17.07	2	26.81	22.2	0.998

样品	温度/℃	失重量/%(mass)	反应级数n	活化能E/(kJ/mol)	指前因子A/min^-1	拟合度r
230N	265—392	52.62	2	76.07	7.75 × 10⁵	0.997
230N	392—528	11.11	2	38.75	4.62 × 10²	0.998
260N	279—386	48.42	2	82.76	2.52 × 10⁶	0.999
260N	386—612	14.91	2	26.96	31.4	0.997
290N	296—390	41.03	2	94.02	1.68 × 10⁷	0.999
290N	390—656	17.07	2	26.81	22.2	0.998

样品	温度/℃	失重量/%	反应级数n	活化能E/(kJ/mol)	指前因子A/min^-1	拟合度r
230N	277～342	40.46	1	80.45	1.53 × 10⁶	0.996
	342～399	13.4	2	28.49	29.89	0.988
	399～481	22.47	1	41.84	200.7	0.964
260N	281～341	39.14	1	81.07	1.52 × 10⁶	0.991
	341～417	19.7	2	27.17	18.14	0.985
	417～497	24.61	1	38.83	96.4	0.964
290N	281～347	32.45	1	97.33	3.31 × 10⁷	0.981
	347～429	23.24	2	18.32	1.28	0.984
	429～495	23.21	1	50.58	831.4	0.99
260CO₂	283～347	41.68	2	99.49	1.02 × 10⁸	0.996
	347～427	18.54	2	27.91	24.4	0.989
	427～487	18.53	1	45.39	359.2	0.964
260O₂	281～346	43.61	2	97.18	6.52 × 10⁷	0.996
	346～429	19.31	2	26.82	18.9	0.984
	429～493	19.34	1	42.17	190.6	0.983