Article pubs.acs.org/est
Bioferment Residue: TG-FTIR Study and Cocombustion in a MSW Incineration Plant Xuguang Jiang,*,† Yuheng Feng,† Guojun Lv,† Yuying Du,† Dianshan Qin,† Xiaodong Li,† Yong Chi,† Jianhua Yan,† and Xudong Liu‡ †
State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou 310027, China Zhejiang Jinhua Conba Bio-Pharm.Co., Ltd
‡
ABSTRACT: With fast development of industry large quantities of hazardous waste are produced in China. Today, incineration plays an important role in the disposal of hazardous waste. Co-incineration of some types of hazardous wastes with municipal solid waste (MSW) has been suggested in the Proposed Standards for Pollutants for MSW combustors in China, published in 2010. According to this proposal, coincinerated hazardous waste should have similar combustion characteristics with MSW, such as bioferment residue (HW02−276− 001−02 in China Hazardous Waste List). In this study, residue from the production of hydrochloride salt spectinomycin, a bioferment process, was studied by thermogravimetric analysis (TGA) coupled with Fourier transform infrared (TG-FTIR) analysis. In TGA, the sample attains its final weight before 800 °C. No gaseous pollutants evolve in large amount during FTIR analysis. During test runs at a MSW incineration plant in Jinhua, Zhejiang Province, bioferment residue was added to MSW at a rate of 24 ton/day and fed to the circulated fluidized bed (CFB) incineration system with capacity of 500 ton/day MSW. The operating parameters and emissions were monitored. The system performance was obviously not affected by addition of bioferment residue to MSW/coal and the pollutant emissions met the Chinese standard, with or without addition of bioferment into feedstock.
1. INTRODUCTION In recent years, the impact of hazardous wastes on the environment and human health has been the object of increasing governmental and public scrutiny.1 According to the statistics of Ministry of Environmental Protection of China, 15 870 000 ton of hazardous waste was produced in 2010, among which around 32% was disposed by incineration or landfill, 61% was reused in industry, and the rest was stored for further disposal or reuse. Incineration has become widely used because of its ability to minimize the weight of waste and of the low levels of secondary pollution. Moreover, with the lack of space for landfills, incineration will play a significant role in the future disposal of hazardous waste. In China, most hazardous wastes are incinerated in plants designed exclusively for hazardous wastes. As in the EU, the system featuring a rotary kiln combined with a secondary combustion chamber is widely used.2 Bioferment residue is a byproduct of pharmaceutical industry. It was defined as a kind of hazardous waste in China Hazardous Waste List, enacted in 2008, and classified under the code of HW02−276−001−02. Co-incineration of hazardous waste is permitted in the EU in a plant not intended primarily for incineration, when some requirements are met (Directive 94/67/EC). In the applicable standard for China (GWKB3−2000) hazardous waste was not permitted to be incinerated in a MSW incinerator. Still, in the Proposed © 2012 American Chemical Society
Standards for Pollutants for MSW Combustors in China, published in 2010, medical waste and bioferment residue were proposed for codisposal in MSW incinerators due to their heattreatment performances similar with domestic waste. The mass of these hazardous wastes fed is required to remain lower than 5% of the capacity of the MSW incinerator. Hence, there is an urgent need analyses the thermal behavior of the bioferment residue. A trial coincineration of bioferment residue in MSW incineration plant is also necessary to understand whether the addition of bioferment residue into MSW as feedstock will affect stable operation and acceptable pollutant emissions of the plant during coincineration. Thermogravimetric analysis (TGA) coupled with Fourier transform infrared analysis (TG-FTIR analysis) is a very useful tool in the analysis of pyrolysis or combustion of solid fuels because both the weight of solid left and the evolution of different volatile gases are monitored continuously during the heating process.3 Weight loss curve (TG curve) and derivative weight loss curve (DTG curve) could be obtained in the TG analysis, in which thermal processes in different temperature ranges could be divided according to the peaks of the DTG Received: Revised: Accepted: Published: 13539
August 8, 2012 November 18, 2012 November 19, 2012 November 19, 2012 dx.doi.org/10.1021/es3032133 | Environ. Sci. Technol. 2012, 46, 13539−13544
Environmental Science & Technology
Article
Table 1. Basic Information of Hydrochloride Salt Spectinomycin Molecule
Table 2. Proximate and Ultimate Analysis and Heat Value of Auxiliary Fuel, Bio-Ferment Residue and MSW (Massive %)a Proximate Analysis (%)
a
item
moisture
ash
volatile
Yanzhou bituminous coal bioferment residue MSW
4.54 49.35 51.56
11.39 5.05 19.21
26.55 40.85 25.79
fixed carbon
lower heating value (J/g)
57.52 4.75 3.44 Ultimate Analysis (%)
combustible fraction
26 882 9146 5581
84.07 45.60 29.23
item
C
H
N
S
O
F
Cl
Yanzhou bituminous coal bioferment residue MSW
69.86 21.58 18.07
3.93 4.30 2.56
1.03 1.11 0.52
0.65 0.28 0.07
8.47 18.26 7.71
0.01 0.03
0.10 0.04 0.30
Results are as-received basis. Analysis was done on Dec 28th, 2011.
washed with spray water. The filtrate was adjusted to pH 6.5− 7.0 using 15−20% NaOH solution and was filtered again. Perlite (3−4 kg/m3) was added as filter aid when necessary. The residue produced during the process consisted of two parts. One was the residue filtered by plate-and-frame press, and the other was perlite residue produced by perlite filter aid. The residue from the production process of hydrochloride salt spectinomycin also belongs to hazardous waste in the European Waste Catalogue and the Hazardous Waste List valid from January 1, 2002, as filter cake and spent absorbents from MFSW of pharmaceuticals with the code 07−05−09. The contents of C and H were determined by the Liebig method (ISO 625−1996). The N content was derived by the semimicro Kjeldahl method (ISO 333−1996). The S content was analyzed by IR spectrometry (ISO 19579−2006). The content of F and Cl were established by combustionhydrolysis/ion chromatography (IC) method. The content of O was found by difference. The result of a proximate and ultimate analysis is listed in Table 2 for the three feed streams. The moisture content of bioferment residue and MSW was around 50% leading to a lower heating value compared with the auxiliary fuel, Yanzhou bituminous coal. Actually, high moisture content and low heating value are key characteristics of MSW in China. A CFB incinerator represents a large thermal flywheel, with 95% of the solids circulating in the incinerator. Strong turbulence in the incinerator and the presence of abundant solid particles, so heat transfer is very efficient. Furthermore, the residence time of unburned particles is multiplied due to their separation and circulation. Because of these advantages, CFB is widely used for combustion of low heating value fuel, such as MSW. To avoid temperature fluctuations in the
curve. From the 3D spectrum FTIR analysis, not only the composition of mixed evolution gases could be identified but also their emission concentration with temperature could be quantified. TG-FTIR analysis is widely used in researching the pyrolysis and combustion of coal,4 biomass,5−7 and hazardous wastes.2,8−10 The cofiring of MSW and coal were investigated previously.11−15 Biomass and sewage sludge are also materials studied in cocombustion.16−20 The laboratory study and industrial operating data of cofiring of hazardous waste with MSW and coal were not reported before. The bioferment residue from a factory of Conba Co. Ltd., a large-scale pharmaceutical company in China, was studied by TG-FTIR analysis to know its thermal behavior in pyrolysis and combustion process. The residue was also added into the feedstock in a MSW incineration plant in Jinhua, to Zhejiang Province, and the data of the emission pollutants were monitored.
2. EXPERIMENTAL SECTION 2.1. Materials. The bioferment residue used in this study was the residue from the production process of hydrochloride salt spectinomycin. It is a drug often given by injection to treat gonorrhea, especially for patients who are allergic to penicillin. The basic information of the molecule is listed in Table 1. In the production process, glucose, starch, corn syrup, fish protein concentrate, yeast, soybean oil, and monopotassium phosphate were first mixed in a fermenter and sterilized by steam. Once being inoculated with funguses, the mixture were stirred and fermented. Around 30 h later, the fermentation liquid was acidified and discharged. Then the acidizing fluids were pumped into a plate-and-frame press to be filtered while 13540
dx.doi.org/10.1021/es3032133 | Environ. Sci. Technol. 2012, 46, 13539−13544
Environmental Science & Technology
Article
Heat transfer from the flue gas produces steam at high temperature (450 °C) and pressure (3.82 MPa). This steam drives a 3000 rpm steam turbine coupled to a 15 MW electricity generator. the acid gas (HCl, HF and SO2) was designed to be treated by the semidry method in the gas scrubber, and activated carbon was to be injected into the flue for adsorption of dioxin and heavy metals in flue gas. However, the acid gaseous pollutants, PM, and dioxin could meet the Chinese limits even without the injection of lime and activated carbon in several months before the experiment. So they are not injected into the flue during the coincineration experiment. The emissions of gaseous pollutants, PM, dioxin, and heavy metals were monitored at a measuring point in the middle of the stack. The concentration of gaseous pollutants (CO, SO2, NOx, HCl and HF) and moisture were measured by an FTIR spectrometer of a portable gas analyzer GASMET Dx-4000 (Temet Instrument Oy, Finland). The concentration of O2 could also be measured by a ZrO oxygen analyzer in GASMET Dx-4000. The PM concentration was determined by a Laoying 3012H PM analyzer. A Pitot tube with a filter was used to gather PM in stack gas by equi-speed. The PM concentration was determined by the weight increase of the filter. Sampling and quantification for PCDD/Fs in the flue gas are carried out according to USEPA Method 0023A. The heavy metals in stack gas were sampled and quantified according to GB18484−2001.
incinerator and ensure the load of the boiler/turbo-generator, bituminous coal is used as auxiliary fuel in the plant. 2.2. Equipment and Method in TG-FTIR Experiment. A TG-FTIR analyzer was used to study the evolution of weight and of Volatile Matter of bioferment during pyrolysis and combustion. A Nicolet Nexus 670 spectrometer and a Mettler Toledo TGA/SDTA851e thermo analyzer were connected by a stainless steel transfer line. Approximately 10 mg of the sample was used in this study. The sample was dried in an oven at 105 °C for 3 h. Then it was crushed to powder finer than 0.2 mm. For most hazardous wastes, 1000 °C is sufficiently high for almost all gas volatile matter to evolve,2,8−10 so 105−1000 °C was set as temperature range and the heating rate was set at 30 °C/min. Nitrogen was used as inert gas during pyrolysis. In FTIR, resolution of the spectrum was set at 4 cm−1 within a wavelength range 4000−400 cm−1, and the scan frequency was 20 times per minute. 2.3. Jinhua MSW Power Plant and Sampling Method. Jinhua is the transit hub of Zhejiang Province. The daily output of MSW in the Jinhua urban area exceeded 450 ton in 2003. In 2005 Zhejiang Bada Jinhua Steam Supply and Power Generation Company Ltd. invested $21 140 000 US to build a MSW incineration plant in Jinhua. The State Key Laboratory of Clean Energy Utilization of Zhejiang University designed the CFB incinerator, with capacity of 500 t/day. The construction work was completed in March 2006 and the combustor started commercial operation in May 2007. Figure 1 displays the schematics of the CFB combustion system of Jinhua MSW incineration plant. It consists of a
3. RESULTS AND DISCUSSION 3.1. TG-FTIR Analysis. The TG and DTG curves of the bioferment residue in combustion and pyrolysis are displayed in Figure 2. The pyrolysis process of the sample could be
Figure 1. Process configuration of the CFB combustion system of Jinhua MSW plant. (1) MSW and bioferment feeder, (2) coal feeder, (3) CFB furnace, (4) cyclone (5) superheater and economizer, (6) air preheater, (7) blower fan, (8) activated carbon feeder, (9) semidry gas scrubber, (10) baghouse filter, (11) quicklime feeder, (12) induceddraft fan, (13) stack. Figure 2. TG and DTG curve for combustion and pyrolysis of bioferment residue.
feeding system, a CFB combustor, a waste heat recovery system, and the pollution control system. Bioferment residue was packed in sealed bags in the pharmaceutical factory, transported to the incineration plant and stored in the bunker, and covered with lime before being fed into the incinerator. Mixed MSW and bioferment residue were fed into the CFB incinerator after shredding. A scraper conveyer fed coal particles as auxiliary fuel into the incinerator yet at a lower point than the feed of waste. The feedstock was heated in the riser by the flame and the high temperature bed material; then evolution of volatile matter and combustion ensued. After staying in the riser for more than 2 s, the high temperature gas entered into the cyclone where coarse ash and unburned particles were separated. The furnace wall acted as radiant heating surface, whereas the vertical flue after cyclone figures as convection heat exchanger.
subdivided into two steps. The first step, fast decomposition, was from the 105 to 639 °C. Two peaks, at 271 and 333 °C, were found in this stage. The second step, the further cracking of fixed carbon, was from 639 °C to the end of the experiment. The weight loss of the sample during the whole pyrolysis process is 70.7%. As well as pyrolysis, the combustion process of the sample could be divided into two stages. The first step, from 105 to 522 °C, was fast decomposition and similar to the pyrolysis process. Before 361 °C, pyrolysis and combustion process have similar DTG curves, which indicates that the presence of oxygen did not accelerate the weight loss of the sample at low temperature. It was observed in the figure the weight loss during pyrolysis was even more than that during combustion from 361 to 558 °C, which means that oxidation of inorganic 13541
dx.doi.org/10.1021/es3032133 | Environ. Sci. Technol. 2012, 46, 13539−13544
Environmental Science & Technology
Article
ingredients of the sample might occur during combustion. The second step, the combustion of fixed carbon, was from 522 to 1000 °C. The total weight loss of the sample during combustion was 80.5%. The DTG curve of this step during combustion became horizontal after 800 °C. Because weight loss of the sample from 800 to 1000 °C was 0.6%, most of the combustible ingredients of bioferment residue was released from the sample before 800 °C. The combustion behavior of municipal solid waste from Guangdong Province, China was studied by TG analysis.21 The TG curve of combustion of MSW was similar to that of bioferment residue. Both reached the highest peak at around 300 °C, and only combustion of carbon residue occurred after 600 °C. In conclusion, the weight loss performances of bioferment residue were similar in pyrolysis and combustion conditions at low temperature. However, at high temperature, the presence of oxygen favored the weight loss of the residue. It is best to maintain over 800 °C with excess air supplied in thermal disposal of bioferment residue. Figure 3 shows the spectrum of pyrolysis emissions from bioferment residue at 271 °C, the temperature with of highest
Table 3. Key Parameters of CFB Incinerator and Power Generation System without coincineration
coincineration
ton/ day ton/ day ton/ day ton/h Mpa °C % ton/ day ton/ day °C
493.2
448.3
0
24
81.8
86.1
60 3.57 439.7 0.5 60.0
54.9 3.52 442 0.4 60.1
59.7.
60.0
872
863
°C
857
853
item
unit
MSW incinerated bioferment residue incinerated coal equivalent (29300 kJ/kg) consumed steam output steam pressure steam temperature loss on ignition of bottom ash fly ash collected from baghouse filter bottom ash average temperature of dense phase zone average temperature of freeboard
for 3 h to determine the loss on ignition of bottom ash. 'The results show the losses on ignition of bottom ash were around 0.5% in both of the conditions, which was far below the limits, 5% in both Chinese and EU standards (GB18485−2001 and Directive 2010/75 EU). This indicates that the most organic compounds were destructed and removed during the combustion in CFB incinerator for both conditions of different feedstock. There are three temperature measuring points in dense phase and two temperature measuring points in freeboard in CFB furnace. The temperature of different potions were averaged and listed in the table. It could be found that the temperature in dense and dilute phase were both in the range of 850−900 °C. Dioxin and organic hazardous content were destructed rapidly in this temperature range.22 From the TG and DTG curves of the combustion process of bioferment, it was found that the weight loss of the sample was almost completed at 800 °C and the weight loss in the time range from 800 to 1000 °C was only 0.6%. So this temperature range was high enough for the destruction of most of the hydrocarbons in bioferment residue. 3.3. Pollutants Emissions. Table 4 summarized the pollution emissions monitored in stack and emission limits of different standards. In China, the pollutant emissions in flue gas from the MSW incineration plant and the hazardous waste incineration plant have to obey their own standards (GB18485−2001 and GB18484−2001), respectively. The standard for hazardous waste (GB18484−2001), which is stricter, was listed here. The limits for feed rate of 300−2500 kg/h were selected. For the European limits, the emission limits set for a plant that coincinerates untreated mixed municipal waste in Directive 2010/75 EU are listed in the table. The American limits are according to the standard for hazardous waste cocombusted in solid fuel boilers in CER-Title40-Part63SubpartEEE of USEPA. All of the emissions and limits were corrected to dry gas, 11% O2, 101.325 KPa, 273.15 K. It was observed in the table that the concentration of SO2, HCl, and HF were under the limits of the Chinese standard even without the application of gas scrubber, and the addition of bioferment residue into the feedstock did not lead to the apparent increases of the pollutant emissions of these gases. In a case study of a 100 ton/day MSW incineration plant in
Figure 3. Infrared spectrum of pyrolysis products from bioferment residue at 271 °C.
peak in the DTG curve during pyrolysis. Only CO2 was found in the spectrum. The same outcome was found in the whole processes of pyrolysis and combustion. No gases could be discriminated in the spectrum except CO2. The contents of Cl in bioferment residue were less than 0.05%, which was much less compared with some hazardous wastes with high content of Cl like PVC. So no HCl were found in the FTIR spectrum. This result means discharge of some common pollutant gases in large quantities would not happen during the thermal disposal of bioferment residue. The addition of bioferment into MSW will not increase the emission of pollutant gases in flue gas. 3.2. Coincineration Performance. On December 12th, 2011, bioferment residue was added into the MSW as feedstock of the CFB to study the influence of the addition to the operation and pollutant emission of the incineration system. The output of the bioferment residue from the pharmaceutical factory of Conba Co. Ltd. in Jinhua was 8 ton/day. Taking the fluctuations of the output into account, the feed rate of the bioferment residue during the test was set at 24 ton/h. On December 13th, 2011, the operating parameters and pollutant emissions were monitored without addition of bioferment into feedstock to be compared with the data in coincineration conditions. The major parameters of the waste incineration system are listed in Table 3. The loss on ignition of bottom ash was measured. The dry bottom ash was combusted at 600 ± 5 °C 13542
dx.doi.org/10.1021/es3032133 | Environ. Sci. Technol. 2012, 46, 13539−13544
Environmental Science & Technology
Article
pollutant emissions of the incineration system apparently. All of the pollutant emissions met the Chinese standard for hazardous waste incineration plant in both of the conditions. But it could also be found that the Chinese standard is far behind the standards of the EU and the USA. With the exception of some heavy metals, none of the pollutant emissions could meet the European and American standards. In the future, some measures should be taken in this plant to meet the international standard. The air distribution needs to be adjusted to avoid the chemical incomplete combustion so that the emission of CO could be controlled. The emission of acid gas (SO2, HCl, and HF) could be reduced if the quicklime is injected into the gas scrubber. The denitration equipment is recommended to be installed to reduce the emission of NOx. The quality of baghouse filter should be improved to meet the stricter standard by Chinese baghouse producer. 3.4. Dioxin Emissions. Incineration of MSW could produce hazardous toxic organic compounds, such as polychlorinated dibenzodioxin and polychlorinated dibenzofuran (PCDD/PCDF). The emissions of PCDD/PCDF before and after baghouse filter in two feedstock conditions were listed in the Table 5. The data were averages over eight hours according to Directive 2010/75 EU. The emission data and standards were corrected to dry gas, 11% O2, 101.325KPa, 273.15K.
Table 4. Pollution Emissions in Flue Gas from 500 ton/day CFB Incinerator at Jinhua MSW Power Plant (Units: mg/N3 in ST) Emissions
item
a
PM CO SO2 NOx HCl HF Hg Cd Pb Cr + Sn + Sb + Mn As + Ni Cd + Ti Sb + As + Pb + Cr + Co + Cu + Mn + Ni + V Pb + Cd As + Be + Cr
no bioferment residue added
bioferment residue added
35.5 76.7 154.2 343.3 12.8 2.7
