Article pubs.acs.org/EF
Cogasification of Biofermenting Residue in a Coal-Water Slurry Gasifier Yuying Du,† Xuguang Jiang,*,† Xiaojun Ma,‡ Lianghua Tang,§ Mingxia Wang,§ Guojun Lv,† Yuqi Jin,† Fei Wang,† Yong Chi,† and Jianhua Yan† †
State Key Laboratory of Clean Energy Utilization, Zhejiang University, 38 Zheda Road, Hangzhou, Zhejiang 310028, People’s Republic of China ‡ Industrial Technology Research Institute, Zhejiang University, 148 Tianmushan Road, Hangzhou, Zhejiang 310028, People’s Republic of China § Zhejiang Fengdeng Chemical Co., Ltd., 20 Chengjiaoxi Road, Lanxi, Zhejiang 321103, People’s Republic of China S Supporting Information *
ABSTRACT: Biofermenting residue (BR) arising from the production of antibiotics was cogasified in an industrial scale MCSG coal-water slurry gasifier. It released large amounts of volatiles during pyrolysis at low temperature (below 650 °C), as follows from thermogravimetric analysis in an inert gas stream. The main evolved volatiles are light gaseous compounds, such as H2O, CO, CO2, and H2 (monitored by MS analysis), and heavy organics with high oxygen content (monitored by FTIR analysis). During industrial scale experimental tests, BR cogasification had little influence on syngas composition, when compared with straight coal-water slurry gasification. The emissions to air from BR cogasification basically meet the emission limits in China. The solid residues produced meet the Chinese requirements of agricultural sludge. Cogasification in a MCSG coal-water slurry gasifier may be a viable alternative solution for BR treatment. However, further research is needed to apply this in other types of gasifiers or to expand the range of waste/biomass cotreatment.
1. INTRODUCTION Gasification is the partial oxidation of material in the presence of oxidant in an amount lower than that required for stoichiometric combustion. It includes a number of sequential steps: drying, pyrolysis, and gasification as well as partial oxidation of the volatiles, tar and char. The combustion provides the heat needed in gasification reactions and needed to maintain the reactor temperature. The obtained syngas has a wide range of applications, such as fuel gases or chemical building blocks. The high temperature (1300 °C or more) and the reducing environment during gasification are supposed to prevent effectively the formation of dioxins, furans, SOX, and NOX in the syngas.1 Besides, gasification could accommodate a wide variety of feedstock;2 it is considered an efficient way of biomass to energy conversion and could be applied in waste/ biomass treatment.3 Over the past two decades biomass gasification has been regarded as a promising technology. Arena4 assessed the gasification of municipal solid waste (MSW) finding gasification a technically viable option for solid waste conversion. However, it is not mature enough to be widely applied in the market.5 Simone6 investigated biomass gasification in a downdraft gasifier and found that biomass could better be used as a complementary feedstock in cogasification with other fuels, to avoid the influence on the performance, productivity, and stability of gasifier. Hong investigated plastic waste cogasification with biomass and found that the overall gasification performance was enhanced.7 Ricketts reviewed cogasification of waste/biomass with coal and found a number of advantages in cogasification of coal and waste/biomass.8 The cogasification of © 2014 American Chemical Society
waste/biomass may offer an alternative to disposal and utilization of waste/biomass. Most studies on waste/biomass cogasification were conducted in gasifiers designed for solid fuels and coupled to an engine or a boiler and turbines. However, waste/biomass cogasification in a coal water-slurry pressure gasifier, as used in most chemical plants in China, was scarcely concerned. The coal-water slurry pressure gasification is a kind of entrained flow gasification technology with a wet feeding system. It is the second generation of coal gasification technology based on the heavy oil gasification. The application of the Texaco coal-water slurry gasification technology was introduced into China in large numbers since the 1990s. In the early 21st century, China’s own coal-water slurry gasification technologies were developed, including the opposed multiburner coal-water slurry gasification, the multicomponent slurry pressure gasification (MCSG), and the multistage nozzle gasification. In China, this technology is mainly applied in the chemical industry, especially in the coal chemical industry. These gasifiers are commercially available for waste/biomass cotreatment. Researchers studied the influence of sewage sludge and algae on coal-water slurry (CWS) properties9−11 but did not refer to the possibility of cogasification. Wang investigated the coslurry properties of coal and semichar from rice stalk pyrolysis and simulated the gasification process,12 however, without conducting experimental tests. Received: December 16, 2013 Revised: February 2, 2014 Published: February 21, 2014 2054
dx.doi.org/10.1021/ef402477j | Energy Fuels 2014, 28, 2054−2058
Energy & Fuels
Article
Table 1. Proximate and Ultimate Analysis, Air Dry Basis coal CWSara BR a
M (%)
A (%)
V (%)
Fc (%)
Ma (%)
LHVa (kJ/kg)
C (%)
H (%)
N (%)
S (%)
O (%)
F (ppm)
Cl (ppm)
2.7 9.9
7.8 4.8 7.7
30.1 18.5 69.6
59.5 36.6 12.9
17.1 40.2 81.9
23890 16602 1541
73.1 45.0 42.8
4.1 6.8 6.1
0.7 0.4 6.0
0.4 0.2 0.2
11.4 41.2 27.4
7.0 4.3 0.0
1012 622 1079
ar, as received basis. molecular weight organic compounds would partly break down into low molecular weight ion fragments, leading to a complicated MS spectrum, which is hard to interpret. Hence, the capillary transfer line and inlet port of MS are both kept at 110 °C so that most of the organics would be condensed from the gaseous products prior to detection. So only the light gas compounds with boiling point below 110 °C would be detected. The mass detection is performed in a scan range of 1−300 amu. 2.3. Cogasification Industrial-Scale Tests. Cogasification experimental tests were conducted in an industrial MCSG coal-water slurry gasifier. The MCSG gasifier employs pure oxygen as a gasifying agent. It operates at a pressure of 1.27 MPa in a temperature range of 1300−1400 °C. The design consumption is 100 t of coal per day. The main parameters of MCSG coal-water slurry gasifier are listed in Table 2.
In this work, cogasification of biofermenting residue (BR) is studied experimentally in an industrial scale MCSG coal-water slurry gasifier. Pyrolysis behavior is studied separately, by microscale thermogravimetric study and analysis of the pyrolysis products by mass spectrometry and FTIR.
2. EXPERIMENTAL METHODS 2.1. Samples. Biofermenting residue (BR) arises mainly in the production of antibiotics. The typical technique of production is as follows. First, a specific strain is fed to a fermentation tank containing a broth of materials such as glucose, starch, fish meal, yeast powder, soybean oil, etc. After fermentation with stirring for 30 h, the broth is acidified and filtered. The filter residue is mainly composed of cell debris and residual product. This BR is identified as a hazardous waste (HW02 Toxicity) according to the National Hazardous Wastes classification, proposed by the Ministry of Environmental Protection of China. The proximate and the ultimate analysis and also the lower heating value (LHV) are shown in Table 1 for both BR and coal. The proximate analysis is based on the Coal Industry Analysis Method (GB/T 212-2008); the ultimate analysis is tested by the elemental analyzer (1ECOCMNS932) and ion chromatography (IC 792); and, the LHV is calculated from the measured calorific bomb higher heating value.13 As can be observed, both coal and BR are mainly composed of carbon (C), hydrogen (H), and oxygen (O). The wet BR (on an as received basis) contains a large amount of moisture (81.9 wt %), while BR (on air-dry basis) contains 9.88 wt % of moisture. The wet BR easily dissolves in water and distributes homogeneously in the coalwater slurry. Yet, BR presents much more volatiles (V) content than coal, indicating the higher reactivity of BR in thermal processes. Hence, BR gasification proceeds already at lower temperature, compared to coal. BR contains no more ash (A) than coal. The LHV of wet BR is quite low, due to its high moisture content. BR has similar sulfur (S), fluorine (F), and chlorine (Cl) contents as coal, yet much higher nitrogen (N) content. Moreover, the high fuel-bound N in BR could lead to high generation of NH3 (and HCN) in the syngas6 rather than NOX, as a result of the reducing atmosphere encountered during gasification. 2.2. TG-FTIR and MS Lab-Scale Tests. Thermogravimetric (TG) analysis provides Supporting Information on the thermal behavior and properties. In this study a Mettler Toledo TGA/SDTA851e thermoanalyzer is used coupled to a Fourier transformed infrared (FTIR) spectrometer (Nicolet Nexus 670) via a pipe kept at 180 °C, to get qualitative information on the pyrolysis generated volatiles. The composition of the gas, largely composed of hydrogen, carbon monoxide and carbon dioxide, as produced during BR pyrolysis, is determined by mass spectrometric (MS) analysis, conducted by connecting a HIDEN QIC-20 Mass Spectrometer to the effluent. The sample of BR (on air-dry basis) is finely ground to achieve better heat transfer.14 In the case of TG-FTIR analysis, about 10 mg of BR sample is heated from 25 to 1000 °C at three distinct heating rates (10, 30, and 50 °C/min). The carrier gas employed is a constant flow of nitrogen (50 mL/min) for pyrolysis tests and a constant flow of air (50 mL/min) for combustion tests. The FTIR gas cell is also heated at 180 °C so that the organics would present in the form of aerosol and be detected by the FTIR.15 The FTIR spectrum has a wavenumber range of 4000−400 cm−1. In the case of MS analysis, about 50 mg of sample is used and heated from 25 to 1000 °C at a heating rate of 30 °C/min. The carrier gas used is a constant flow of helium (He) for pyrolysis test and a constant flow of air for combustion test. The high
Table 2. Characteristics of the MCSG Coal-Water Slurry Gasifier parameter
value
reactor size reaction environment feedstock coal consumption gasifying agent reactor pressure reactor temperature
φ2400 mm ×8000 mm reducing coal-water slurry 100 t/D 99.6% pure oxygen 1.27 MPa 1300−1400 °C
The flow sheet of the gasifier is shown in Figure 1. First, the additive used in the preparation of coal-water slurry (CWS) is diluted with
Figure 1. Flow sheet of the MCSG coal-water slurry gasifier.
wastewater from pharmacy manufacturing in a dilution tank. The proportion of additive to coal is about 6:1000. Then the resulting mixture wastewater is pumped to a wet ball mill where the coal is milled and further mixed with the diluent, and CWS is prepared and then pumped to a CWS tank for intermediate storage. In the tests, proximately 5 ton of coal is fed per hour. Properties of coal and CWS are reported in Table 1 and that of wastewater in Table 3. In the case of BR cogasification in gasifier, wet BR is mixed with the wastewater in a dissolving tank, and the produced BR wastewater diluent is added to dilution tank. The proportion of coal, wastewater, and wet BR added are approximately 65:30:5. The feed rate of wet BR (i.e., BR on an as received basis) is about 385 kg/h. The equivalent feed rate for BR (i.e., BR on an air-dry basis) is 77.3 kg/h as calculated according to the following formula 2055
dx.doi.org/10.1021/ef402477j | Energy Fuels 2014, 28, 2054−2058
Energy & Fuels
Article
Table 3. Property of the Wastewater from Pharmacy Manufacture, mg/La pH
CODMn
chloride
fluoride
Pb
As
Cu
22.9 Zn
