VILLAGE OF SALTAIRE INCINERATOR
AIR POLLUTION CONTROL TECHNOLOGY EVALUATION
AND CONCEPTUAL DESIGN
THE INCORPORATED VILLAGE OF SALTAIRE, NEW YORK
DVIRKA AND BARTILUCCI CONSULTING ENGINEERS
WOODBURY, NEW YORK
An inspection of the incinerator and the air pollution control system was conducted by representatives of D&B on June 14, 1999. The incinerator is a mass burn refractory unit supplied by Morse Bougler and designed to combust 1,000 lb/hr of refuse. The air pollution control system, also supplied by Morse Boulger, consists of a wet scrubber designed to cool the exhaust gases and to control particulate matter. The wet scrubber contains a quench chamber with nozzles which inject water. As water is injected, it impacts with and absorbs particles entrained in the incinerator exhaust gas. The exhaust gas is first directed downward and then upward utilizing a baffle plate. As gases are directed downward, the wetted particles settle and are collected in a water tank located below the scrubber. Periodically, water is drained from the tank and the remaining particulate ash is removed. As reported by representatives of the Village, the wet scrubber is in poor condition and in need of replacement. At the site inspection, representatives of D&B observed the release of a wet oil-like substance from the stack, which is indicative of particulate break-through in the scrubber.
2.0 MINIMUM PERFORMANCE REQUIREMENTS
In order to establish minimum performance requirements for the evaluation of air pollution control technologies, a review of potentially applicable regulations was conducted. A description of each regulation and its applicability to the Village of Saltaire Incinerator follows.
40 CFR 60 Subpart E - Standards of Performance for Incinerators
New Source Performance Standards (NSPS) were established for solid waste incinerators which commenced construction or modification after August 17, 1971. This regulation is applicable to incinerators which have a charging rate greater than 50 tons per day. Since the Village of Saltaire incinerator has a charging rate of 1,000 lb/hr (i.e., 12 tons/day) this regulation is not applicable.
40 CFR 60 Subpart BBBB – Emission Guidelines for Existing Sources: Small Municipal Waste Combustor Units
On December 19, 1995, USEPA promulgated emission guidelines applicable to existing municipal waste combustor (MWC) units. These guidelines were applicable to MWC units located at plants with a capacity greater than approximately 39 tons per day. Due to a court decision, the regulations were restricted to units with a capacity greater than 250 tons per day. On August 30, 1999, USEPA proposed new guidelines for existing facilities with small MWC units. The proposed guidelines, which are subject to public review and comment, will apply to MWC units with a capacity greater than 35 tons per day and less than or equal to 250 tons per day. Therefore, it appears that the emission guidelines will not be applicable to the Village of Saltaire Incinerator, since its capacity is less than 35 tons/day.
6 NYCRR Part 201 – Permits and Registrations
In New York State, air permits are issued pursuant to 6 NYCRR Part 201. These regulations apply to major facilities subject to Title V (incorporating the federal Title V operating permit regulations) as well as minor facilities. Based on the maximum potential to emit of the Saltaire Incinerator, it does not exceed any of the Title V major source thresholds, and is therefore classified as a minor facility.
The Village of Saltaire was issued a certificate to operate by NYSDEC following construction of the incinerator in the 1970s. On May 2, 1996, NYSDEC notified the Village that the certificate to operate was extended to May 15, 2001, under the state’s Part 201 transition program. The certificate to operate does not contain any special conditions limiting incinerator operations or the emissions of any pollutant.
As a minor facility with an existing certificate to operate, any proposed modifications to the incinerator would be subject to the requirements of 6 NYCRR Part 201-5 (State Facility Permits). Under 6 NYCRR Part 201-5.4, an application for a permit modification must be made under the following circumstances:
A "modification" is defined in 6 NYCRR Part 200.1(ao) as "Any physical change or change in the method of operation of an incinerator, stationary combustion installation or process which…increases the hourly emission rate, emission concentration or emission opacity of any air contaminant,…involves the installation or alteration of any air cleaning installation, air cleaning device or control equipment,…or…results in the emission of any air pollutant not previously emitted or authorized under the permit." Under the above definition, the following changes are not considered a modification:
In addition, certain activities defined as modifications may be made to allow for operational flexibility without receiving prior approval of NYSDEC and do not require modification of the permit. The facility must, however, maintain records of the date and description of such changes and make such records available for review by NYSDEC representatives. The changes are summarized as follows:
The following changes can also be made without modifying the permit, but require notification at least 30 days in advance and must meet the operational flexibility criteria described above:
Therefore, replacement of the existing wet scrubber with an alternative pollution control technology of equal or greater particulate control efficiency should not trigger a permit modification. NYSDEC would require a permit modification or further review only if it determines that the modification does not fall under the activities excluded from permit modifications under the operational flexibility provisions, or if the modification is otherwise determined to cause a significant air quality impact.
6 NYCRR Part 219 – Incinerators
Solid waste incinerators are regulated pursuant to 6 NYCRR Part 219. Part 219-5 regulates existing incinerators located outside of New York City or Nassau or Westchester Counties.
Part 219-5 establishes limits on particulate matter. Incinerators with a charging capacity of 2,000 lb/hr or less and constructed after January 1, 1968, must not emit particulate matter exceeding a limit determined according to a logarithmic scale. Based on the incinerator design capacity (1,000 lb/hr), the applicable emission limit is 3 lb/hr.
In addition, for any incinerator subject to Part 219-5 and constructed after January 26, 1967, the average opacity during any 6 consecutive minutes must not exceed 20 percent under normal conditions. Opacity is a measurement of the optical density of a source discharge (plume) and is often used as a visible indicator of particulate emissions. Opacity is measured using either an opacity monitor installed in an exhaust or by a trained observer. When measured by an observer, opacity is determined by observing a plume against a contrasting background and is reported as a range from 0 percent (not visible) to 100 percent (completely obscuring) in increments of 5 percent.
Based on the applicable regulatory criteria identified above, the minimum performance criteria was established as 20 percent opacity. However, vendors were requested to propose a system which under normal operation would produce minimal visible emissions at the incinerator stack, since this is the primary concern to the Village.
3.0 TECHNOLOGY EVALUATION AND CONCEPTUAL DESIGN
A total of six air pollution control vendors were contacted to provide a technical proposal, including budgetary cost estimate and scope of services, for controlling particulates emitted by the Village of Saltaire Incinerator. In order to select proper equipment sizing and estimated operating parameters, vendors were provided with basic design information (e.g., exhaust gas flow rate, temperature and uncontrolled particulate concentration). Provided below is a summary of vendors and the associated APC technology proposed.
McGill Air Clean
Dry Electrostatic Precipitator
Dry Electrostatic Precipitator
Wet Electrostatic Precipitator
Wet Electrostatic Precipitator
Multi-State Venturi Scrubber
Venturi Cyclonic Scrubber
In addition to the control technologies identified above, fabric filters, a technology widely used for control of particulate matter from municipal waste incinerators, was considered. However, this technology was not determined to be practical for application to the Saltaire Incinerator due to the potential damage from "blinding" resulting from moisture and acid gases condensing on the filter surface as the incinerator gases cool after completion of an operating shift. Therefore, fabric filter technology was not considered a viable technology for this facility.
Following receipt of technical/product information from the vendors listed above, the information was reviewed in order to compare the different control technologies available. The following is meant to provide a general description of the air pollution control technologies considered as part of this evaluation, as well as the advantages and disadvantages of each.
Dry Electrostatic Precipitators
Description: Dry electrostatic precipitators (ESPs) have been used for years on municipal waste combustors, as well as other combustion and industrial sources. In a dry ESP, the exhaust gases pass through a chamber where electrodes impart a negative charge to the particulate matter in the exhaust gas stream. These electrodes are negatively charged and are provided with DC voltage. Parallel with the flow of gases through the chamber are plates with a positive electrical charge. The negatively charged particulate matter is attracted by the positive electrical force to one of the plates. Periodically, the buildup of particulate matter on the plates is removed by rapping the plates, causing the particulate matter to fall to the bottom of the chamber where it is removed. The level of particulate control is dependent on the number of chamber sections, or "fields," that the exhaust gases pass through.
Depending on the resistivity of the ash, the particulate size distribution and the temperature, removal efficiencies of up to 99 percent are typically achievable.
Advantages/Disadvantages: Dry ESPs have certain advantages over other types of air pollution control devices. They do not use water and, therefore, there is no requirement to provide clean water or treat and/or dispose of used process water. Compared to medium or high pressure drop venturi-type wet scrubbers, ESPs use much less electric power.
There are also several disadvantages to the use of dry ESPs. The inlet gases to the precipitator must be cooled to less than 600°F (320°C) to prevent plate warping. This requires the use of a heat removal device such as a quench chamber or waste heat recovery boiler. In addition, the exhaust gases must be relatively free of volatile organic compounds (VOCs) to prevent particulate matter from sticking to the plates. It is also desirable to minimize the moisture content in the exhaust gases because the moisture allows discharging of the electrical charge between the electrode and plates and prevents a high charge buildup on the particles. Excess moisture can lead to clogging at the inlet distribution plate to the precipitator, which upsets the flow pattern through the unit. Clogging can usually be detected by monitoring the electrical functions of the device. Voltage and current measurements of the various plates and fields will indicate the gradual buildup of particulates and degradation of performance. During startup of the unit, warm exhaust gases enter the precipitator. This can cause the formation of water or water and acid droplets which could cause severe corrosion in the unit. This situation is usually handled by installing a bypass, which would be used during startup, or the unit is preheated before entry of exhaust gases is allowed.
Wet Electrostatic Precipitators
Description: A wet ESP operates similarly to the dry ESP with the addition of a washing mechanism to counteract the buildup of volatile or particulate matter on the plates. The wet ESP operates like the dry ESP in that there are electrodes to charge the incoming gas particles and plates that are positively charged to attract those particles. However, wet ESPs use a washing system that either periodically or continuously washes the plates with a water system. Wet ESPs have been installed on sewage sludge and hospital waste incinerators downstream of wet scrubbers as a polishing step for control of heavy metals.
The performance of the wet ESP should be equal to or better than the dry ESP. Collection efficiencies of 99 percent or more can be expected.
Advantages/Disadvantages: The advantages of a wet ESP are:
A disadvantage of the wet ESP is the higher operational cost because of the water usage for plate cleansing. Also, the wet ESP collects the particulate matter in a liquid form which requires clarification to remove the particles from the discharged water.
Wet ESPs do not use a rapping system to remove particles from the plates. In these instances, the normal maintenance procedures for wet scrubbers and venturi systems apply to wet ESPs as they pertain to water flow monitoring and control.
Description: Venturi scrubbers are commonly utilized to control particulates from hospital waste and sewage sludge incinerators. The venturi throat, installed in the duct work at the exhaust from a furnace or incinerator, greatly increases the exhaust gas velocity while adding water. The extremely high velocity atomizes the water droplets and increases the surface area available for impacting particulate matter. The "wetted" particulates exiting the venturi throat have a greater mass and size. The particulate-laden water droplets enter a scrubber device where they are effectively removed. The most common venturi throat has a rectangular throat and is equipped with one or two bomb-bay dampers which allow the opening to be varied. A circular throat device, which incorporates a cone nozzle to vary the opening, can also be used. Other types of units operate with a fixed throat and maintain a fairly constant pressure drop across the throat by varying the amount of water added as gas flow changes.
Depending upon the pressure drop, venturi throats can assist in removing particulate down to approximately 0.5 microns in diameter. Pressure drops typically range from 20 to 30 inches of water with another 10 inches of water for the scrubber/separator, for a total pressure drop at the induced draft fan of approximately 30 to 40 inches of water.
Advantages/Disadvantages: The venturi throat is a relatively effective particulate wetting device if the pressure drop can be adjusted to obtain the removal efficiency desired. A properly designed unit should have a variable aperture to permit stable removal efficiencies while the gas volume processed by the system varies.
The venturi throat system uses a significant amount of water, which requires a clean water source and a disposal point for the processed water. In addition, as the control efficiencies increase, the pressure drop across the scrubber increases. This can create a significant electrical load which results in a high operating cost. Higher pressure also creates higher stresses for the induced draft fan, creating a maintenance concern.
Maintenance of the venturi throat should be minimal if adequate waterflows are maintained to the cone section. If adequate water is not provided, these areas may erode. Normal maintenance should be performed on the adjustment mechanism that modulates the damper blades.
A table summarizing the major equipment, operation and performance characteristics associated with each control system is presented in Table 1.
A brief summary of each proposal is provided below.
McGill Air Clean Dry ESP
The system proposed by McGill Air Clean consists of an evaporative cooler to provide for cooling of exhaust gases to approximately 350°F, followed by a two field dry ESP. The vendor indicated that the dry ESP would be capable of achieving less than 20% opacity, as well as a particulate emission concentration of less than 0.04 grains per dry standard cubic foot (gr/dscf). The emission concentration guarantee, when converted to an emission rate is equal to 1.03 lb/hr, using estimated gas characteristics calculated by D&B. This is about 1/3 of the NYSDEC emission limit of 3 lb/hr. However, McGill Air Clean did not believe that the proposed system would survive many years of operation due to the current practice of shutting down the incinerator ("cold" shutdown) at the conclusion of an operating shift, which would cause temperatures in the ESP to drop below the acid gas dew points (even if more costly corrosion-resistant material was substituted). The solution proposed by McGill Air Clean would be to operate the auxiliary burners continuously during periods when the incinerator is not operating. This would represent an increased operating expense, and furthermore, may present a difficulty with some aspects of current incineration operation (e.g., incinerator access for bottom ash removal).
PPC industries selected a dry ESP for its proposed system. PPC also manufactures wet ESPs, but would not recommend them for this application due to anticipated problems due to corrosion from condensation of acid gases. The PPC design consists of an evaporative cooler followed by a single field unit. (PPC does not usually manufacture the evaporative cooler and recommended the TurboTak gas scrubber, which is part of the TurboSonic proposal - see below.) To prevent acid gas corrosion, PPC recommended either injecting sodium bicarbonate prior to shutdown, or operating the auxiliary burners continuously. The sodium bicarbonate would coat the ESP interior and neutralize the acid gases in the incinerator exhaust air. PPC indicated this approach is being utilized at a municipal waste incinerator in Juneau, Alaska. PPC’s performance guarantees consisted of less than 10% opacity and less than 0.05 gr/dscf (estimated to be equivalent to 1.29 lb/hr).
Croll-Reynolds Wet ESP
The Croll-Reynolds proposed system includes a quench section for cooling the incinerator gases followed by a wet ESP. The wet ESP is an upflow design featuring a multi-rod scrubber followed by wet ESP section contained within a single structure. Croll Reynolds indicated their system would be capable of achieving "near zero visible emissions" and guaranteed a minimum of 99% control of particulate emissions, which, based on the design parameters provided by D&B, is equivalent to 0.02 gr/dscf, or 0.52 lb/hr.
TurboSonic Wet ESP
The TurboSonic proposal consists of an evaporative cooler (gas quencher), a separate low energy scrubber for control of large particulate and a wet ESP for control of fine particulate. The wet ESP is a hex tube down flow design. The vendor has guaranteed the particulate emission concentration to less than 0.0075 gr/dscf (estimated to be equivalent to 0.19 lb/hr), which is a much lower emission limit than the other vendor proposals.
Anderson 2000 Venturi Scrubber
The Anderson 2000 system utilizes a multi-stage venturi scrubber system. Gases are first cooled in a quench section. Excess liquid from the quench section discharges into a recirculation tank. The cooled exhaust gases then pass through three venturi sections mounted in series. Gases then are directed to a chevron type mist eliminator. After exiting the mist eliminator, gases enter a subcooling system to reduce the temperature to below 120°F. The system also includes a new ID fan and a 20-foot high exhaust stack. The vendor guaranteed particulate emissions to less than 0.03 gr/dscf, corrected to 7 percent oxygen (estimated to be equivalent to 0.58 lb/hr).
JK Environmental Venturi Cyclonic Scrubber
The JK Environmental proposed system consists of the replacement of the existing wet scrubber with a low-energy "venturi cyclonic" scrubber. A quench section would be installed to cool gases to approximately 300°F to 400°F using water injection. The scrubber pressure drop is set using a damper plate at the inlet to the separator section. Particulates would be collected below the separator section using the existing water tank. The scrubber also includes an ID fan which is mounted on top of the unit. JK Environmental’s proposal also includes a programmable logic controller (PLC) to control the ID fan and scrubber, as well as the combustion air inlet dampers for the incinerator. All of the equipment would be located within the existing building. According to JK Environmental, the scrubber would generate a small wastewater discharge which would be piped to the existing open tank trough.
JK Environmental stated their system would meet the 20% opacity limit. Regarding specific particulate emission performance JK provided test results performed on a hospital waste incinerator located in Queens, New York that is equipped with the same type of scrubber. The test results were reported in units of pounds of particulate emitted per hour. Assuming that similar performance would be achieved if installed at the Village of Saltaire Incinerator, the estimated emission rate would be 1.46 lb/hr. In addition, using the estimated exhaust flow characteristics for the Village of Saltaire Incinerator, D&B has calculated that the venturi cyclonic scrubber would control particulate emissions to approximately 0.057 gr/dscf.
4.0 BUDGETARY COST ESTIMATES
A summary of the estimated capital and annual operating costs for each of the evaluated systems is presented in Table 2. The budgetary cost summary was prepared using the cost proposals submitted by the system vendors supplemented by estimated equipment and/or installation costs.
As indicated in Table 2, the capital cost estimates, with the exception of the venturi cyclonic scrubber proposed by JK Environmental, are significantly higher than the reported cost previously incurred for the replacement of the incinerator wet scrubber. Some reasons for the cost discrepancy are provided below:
Our findings are as follows:
Our recommendations are as follows:
It should be noted that while replacement of the existing wet scrubber using any of the control technologies evaluated in this report will improve particulate control, problems with the incinerator combustion system (e.g., combustion air, auxiliary burners) may cause temporary increases in particulate emissions which are not indicative of normal conditions. In such situations, the new pollution control equipment would not be expected to operate at peak efficiency, and a visible stack condition may occur.See Table 1 - Scrubber Alternatives