DRY SYSTEM EMISSION CONTROL FOR MUNICIPAL INCINERATORS

Transcription

1 DRY SYSTEM EMISSION CONTROL FOR MUNICIPAL INCINERATORS AARON J. TELLER Teller Environmental Systems, Inc. Worcester, Massachusetts ABSTRACT The control of gaseous and particulate emissions from municipal incinerators well within regulatory limits, with essentially zero opacity, requiring skills already available in the facility, and with a solid discharge has been demonstrated in commercial installations in the U.S.A. and Japan. INTRODUCTION The disposal of municipal waste is a microcosm of our total pollution problem. The mere disposal of the waste creates additional pollution problems. Landfill creates leaching pollution. Reduction of volume by combustion creates air pollution and solid waste disposal. Scrubbing creates liquid waste. Yet, as in all other pollution problems, recovery of useful values can be achieved, thermal value by incineration, materials recovery by sorting and separation. The most effective process for disposal of solid waste thus far developed is incineration, often coupled with thermal recovery. A significant reduction in mass is achieved and heat is recovered. There are still, however, gaseous and particulate emissions that must be contained. The noxious gaseous emissions and the range of concentrations encountered are: Compound ppm HO S HF 3-30 The particulate concentration is of the order of 5 g/nm3 with a significant level (> 30 percent) of sub micron particulate. The higher concentrations of HCI ( 1000 ppm) are generally present in the combustion gases emitted in European and Japanese incinerators. The concentrations of HCI in U.S. and Canadian incinerators are, at present, of the order of ppm. The indications are that these will rise as the trend toward plastic packaging inqeases to the level present in European and Japanese incinerators, Regulations regarding HCI emissions are: Japan Germany Italy U.S.A. 250 ppm 200 ppm 50 ppm No Federal requirements In the U.S., particulate emissions are restricted by EPA to 0.22 g/nm3 corrected to 12 percent CO2 for existing incinerators and 0.18 g/nm3 corrected to 12 percent CO2 for new installations. With normal good practice for incinerator operation these values are equivalent to g/nm3 and 0.09 g/nm3 respectively for the outlet gas. Some states are more restrictive with permissible emissions as low as 50 percent of the recommended EPA regulations. Opacity is generally restricted to less than 20 percent. European and Japanese practice in meeting the particulate and acid gas regulations had been the 581

2 use of electrostatic precipitators for particulate removal followed by wet scrubbing for the removal of acid gases. This practice is frowned upon by authorities because of the requirement for discharge of liquid waste and the appearance of a pervasive plume if the particulate is not reduced below 0.04 g/nm3 and acid gas concentrations below 20 ppm. Thus, a more acceptable and more economically viable process was required in order to meet the regulatory requirements and the financial capability of the comm unities, the producers of solid waste. The criteria for an emission control system for incineration are as follows: 1. Compatibility with skills available in the operators of incinerators. 2. Reduction of particulate emissions to levels consistently below the regulatory requirements. 3. Future capability for reduction of acid gas emissions to levels below the most stringent require- ments established in other countries., 4. Reduction of visible plume to opacities below 10 percent. 5. Prevention of liquid discharge. The reasons for these criteria are as follows: TABLE 1 SYSTEM CHARACTERISTICS FOR MUNICIPAL INCINERATOR EMISSION CONTROL Compatibility Particulate Acid Gas Plume Discharge Material handling skills Emissions less than 0.1 g/nm' (corr. 12 percent CO2 ) Emissions less than 10 ppm Less than 10 percent To be solid 1. Compatibility - If new skills are required beyond material handling, additional manpower must bt; added. A three-man addition is equivalent to a capital investment of $750,000 per installation. 2. Particulate - The trend in incinerator regulation based on state of the art is toward a particulate level of 0.1 g/nm3 corrected to 12 percent CO2, In addition, emissions above 0.04 g/nm3 will result in a visible stack emission because of nucleation of the particulates in the humid exhaust. 3. Gas Emissions - Inasmuch as other countries and individual communities have already placed restrictions on acid gas emissions and EPA is now evaluating the technology, there will probably be government pressure to control these emissions in the near future. In addition, high concentrations of acid gases in a humid stack result in an intensification of plume appearance. 4. Plume Appearance - The opacity of a steam plume is a function of particulate and acid gas content as well as ambient conditions. Since the inherent humidity in incineration is equivalent to a dew point range of F (66C-88C), the potential for plume appearance even without additional humidification is high. 5. liquid Discharge - The original mode of acid gas recovery was via scrubbing subsequent to an electrostatic precipitator. This not only resulted in plume intensification but a complex water treatment system as well as discharge of soluble chloride and fluoride salts. Both Japan and Germany have placed approval restrictions on such installations. As a result of this evaluation, it was determined that a dry scrubbing system was essential to meet all the criteria. The system consists of the following components [1-3] (Fig. 1). 1. Quench Reaction - The simultaneous reduction in temperature and neutralization of acid gases by a size-temperature responsive spray of a neutralizing agent, resulting in a dry particulate product at the outlet of the unit. 2. Sub micron particulate capture in the duct via use of a "dry venturi" providing the efficiency of particulate capture equivalent to an 80 in. w.g. (20 kpa) wet venturi but operating at a 1/2 in w.g. (0.1 kpa) pressure drop. 3. Filtration of the entire gas by a baghouse or an electrostatic precipitator. Because of the removal of acid gases the acid dew point no longer controls the operating temperature of the electrostatic precipitator. The proprietary quench reactor (upflow with large particulate removal or downflow) has a responsive droplet size mechanism such that lower inlet temperatures result in the formation of smaller droplets. Inasmuch as vaporization rates are lower with, lower inlet temperatures, the smaller droplet size compensates for this decrease in kinetics, thus establishing consistent performance. The dry venturi, [4] installed as a spool piece in the duct provides for the capture of the hydrophobic submicron particulates at a pressure drop of * in. w.g. (0.1 kpa) with a capture efficiency equal to that achieved in an 80 in. w.g. (20 kpa) pressure drop wet venturi (Table 2). The targets are solid and available locally. 582

3 _ J Reagent Loadin VI 00 w Xl:! 'h--r::r, '1b Erntm,, agilwse or E.P. I xc L 'ii:5isam Injection Sl ctern n. " lol FIG.l FLOW SHEET WITH BUGHOUSE AND ELECTROSTATIC PRECIPITATOR

4 TABLE 2 COMPARISON OF PREDICTED CAPTURE PERFORMANCE: Wet Venturi and Dry Venturi TABLE 3 TOTAL OPERATING COSTS - TELLER EMISSION CONTROL SYSTEM - MUNICIPAL INCINERATORS (BAGHOUSE) Particle Size Wet Venturi Dry Venturi Capture Captured 6P Efficiency 6P Efficiency Microns mm H2O Percent mm H2O Percent $/yr Less Amortization O.:l The neutral salts created in the quench reactor, the agglomerated particulates from the dry venturi, and the superrrucron particulates from the incinerator may now be removed from the gas stream by either a baghouse or an electrostatic precipitator. Lime ($35/ton) 6, Power ($0.03/kWh) 58, TESISORB ($35/ton) 18, Amortization (15 year) 133, Labor ($20,000/MY) 20, Maintenance 25, Total 261, (3.193/t) (1.565/t) If no precipitator is presently installed, the baghouse is preferred. The bases are lower capital cost and acid gas removal. In conjunction with dry venturi operation, the baghouse shake cycle is extended to hr inasmuch as the major portion of the submicron particulates are agglomerated. Thus, the rate of pressure drop rise is minimal and the shake cycle is FIG.2 ISOGO PILOT UNIT 584

5 OPERATION: TELLER SYSTEM MUNICIPAL INCINERAT OR I SOGO - YOKOHAMA, -If'; h (') 400 o z (') IT! Z -i lj - o z - z 300 LI,L INLET - TELLER SYSTEM (FROM INCINERATOR) v, V c> 20 l> (f) " 'Q 'Q 3 10 OUTLET-TELLER SYSTEM o I" TIME FROM START (MINUTES) 135 FIG. 3 ISOGO Hel TESTS small. As a result, a thick cake is created in the baghouse. The result is a flywheel effect. It is known that the acid gas emissions from an incinerator are highly variable. If all of the neutralization is to be conducted in the quench reactor, then either the quantity of neutralizing agent must be introduced responsively to the inlet concentration or, in order to avoid the unreliability of analytical instrument response, the neutralizing agent feed rate must be fed at the maximum requirement. However, because the Teller system permits a buildup of solids in the baghouse, an average rate of reagent feed is permissible. During low acid gas emission periods, the excess reagent accumulates in the cake, and is available for reaction during high acid gas emission periods. The behavior pattern of a constant system emission with variable inlets was observed in pilot tests at Isogo, Yokohama (Figs. 2 and 3). The overall acid gas performance for the baghouse system is reduction from ppm HCI to 3-6 ppm and ppm S02 to 5-30 ppm. Particulate emissions are of the order of 0.06 g/nm3 corrected to 12 percent CO2. Where an electrostatic precipitator is used as the final downstream collector, the acid gas performance is still within acceptable range with a 90 percent efficiency for HCI and an 85 percent efficiency for S02. The system (Fig. 1) has the following characteristics; 1. Compatibility Primarily solids handling one shjrry handling system 2. Particulate Emissions less than 50 percent of present requirements (EPA) 3. Gas Emissions Approximately 15 percent of the lowest required internationally 4. Plume Appearance Zero opacity when the ambient temperature 585

6 is above 50F (loc). With ambient temperature below 50F (10C) a disconnected steam plume is evident with a life of approximately 100 ft (30 m). TABLE 4 TOTAL OPERATING COSTS - TELLER EMISSION CONTROL SYSTEM - MUNICIPAL INCINERATORS - ELECTROSTATIC PRECIPITATOR 5. Discharge Solid product - free flowing. The overall system pressure drop is approximately 8 in. w.g. (1.99 kpa). For a 300 tpd (272 tid) municipal incinerator the estimated operating costs for 300 operating dayslyr are shown in Table 3. For retrofit of an existing electrostatic precipitator installation, costs are shown in Table 4. $/yr Lime ($35/ton) 10,000 Power ($0.03/kWh) 40,000 TESISORB 18,000 Amortization (15 year) 180,000 Labor ($20,ooO/year) 20,000 Maintenance 80, Less Amortiza tion Total 348, (4.259/t) (2.055/t) "If not paid off prior to installation of Teller components. FIG. 4 FRAMINGHAM INSTALLATION Thus total emission control compatible with the needs of the community and with acceptable discharge from aesthetic, pollutant, and by product characteristics can be achieved within reasonable economic limits. This has been demonstrated on a 300 tpd (272 tid) municipal incinerator in Framingham, Massachusetts (F ig. 4) and a 150 tpd (136 tid) municipal incinerator at Yokohama, Japan. Key Words Absorption Dust Emission Envi ronment Gases Incineration Pollution 586