SCR systems require a minimum temperature of approximately 575°F for the destruction of NOx. For applications where the process or equipment burns biomass fuels, a particulate control device is usually needed upstream of the SCR for it to function properly. However, by the time the flue gases pass through the particulate control device their temperature range is much less than required (between 57 and 61 percent) for the SCR to operate effectively. The traditional solution would be to install a natural-gas or oil fired burner between the SCR and particulate control device to re-heat the air to the appropriate temperatures. The economic burden of the capital costs associated with this control scenario, as well as the cost of the fuel required to operate the burners, is not cost effective given the amount of NOx removed.

As a solution, Babcock Power teamed with Pro-Environmental, Inc. (PEI) to combine Babcock’s SCR expertise with PEI’s Regenerative Thermal Oxidation (RTO) technology, capable of achieving heat recovery efficiencies of greater than 95 percent, to produce the RSCR technology. In 2005, a RSCR system installed at a 50MW power plant fired by wood and construction/demolition waste achieved a NOx emission rate of 0.07-lb/mmBTU. This emission rate equates to an 86% reduction in NOx emissions from wood waste combustion (AP-42 Chapter 1.6, Table 1.6-2 “Dry wood-fired boilers”).

If you would like more information on RSCR techology, visit Babcock Power’s website.

If you would like help completing your BACT Analysis, or any portion thereof, feel free to contact me.

According to the 1990 EPA NSR Workshop Manual, in order to show that a control scenario is technically infeasible you must “clearly document and show, based on chemical, physical, and engineering principles, that technical difficulties would preclude the successful use of the control option on the emission unit under review”.

Here is an example:

Our client wanted to install a 6-MW Biomass Boiler to supply process heat for the greenhouses at their facility. Because of the potential emissions from the proposed emission unit, our client was required to perform a BACT Analysis for PM, PM10, NOx, and CO.

One of the control devices identified for the control of particulate matter (PM and PM10) from the boiler was a fabric filter, also known as a baghouse. Although baghouses are used to control particulate emissions from biomass boilers, they are typically installed on larger units at facilities which have full-time boiler staff (1). If left unmonitored, burning cinders, temperature excursions, and/or operating upsets could result in a fire (2). Our client did not have a full-time boiler staff and therefore using a baghouse to control particulates from the proposed boiler was deemed technically infeasible.

If you have questions regarding the technical feasibility of the control technologies that you have identified, feel free to contact Brandon Mogan at (803) 422-5251, or click here for more information.

(1) Resource Systems Group, Inc.
(2) Hog Fuel Boiler RACT Determination. Washington State Department of Ecology. Doc. No. 03-02-009

• Control Devices
• Alternative source operating scenarios
• Alternative fuel combustion techniques
• Control technologies that have been applied to similar emission units

The list of potentially applicable control technologies should be comprehensive. It should include every control scenario from that which provides the most pollutant control (typically LAER) to that which provides the least pollutant control. When generating this list, one must consider all sources of information, including but not limited to:

• EPA’s RACT/BACT/LAER Clearinghouse
• EPA/State air quality permits
• Federal/State air emission inventories
• Control equipment vendors
• Manufacturer’s and trade associations
• International and foreign environmental agencies
• Inspection/Performance test reports
• Technical papers and journals
• Pollution prevention resources

The process of identifying applicable control technologies is a tedious and in-depth process. There are, however, some on-line resources available that offer a good starting point for this purpose. The following is a review of some more commonly referenced sources for identifying control technologies.

EPA’s RACT/BACT/LAER Clearinghouse

The Environmental Protection Agency’s (EPA’s) RACT/BACT/LAER Clearinghouse (RBLC) is a database of best available control technologies that have been applied to reduce emissions of air pollutants. As seen below, it is set up in a very user friendly fasion:

RBLC Database Search

This image is of a “find lowest emission rate” search for carbon monoxide (CO) emissions from a commercial size wood-fired boiler. This search results in the following results:

RBLC Database Search

From this search we have identified two different facilities which have applied best available control technologies for carbon monoxide emissions from their wood-fired boilers. To get more information about the type of control technology, the user must simply click on the “create report” button.

From project experience, I have found that the RBLC is very incomplete and limiting your search to control technologies found in the RBLC is not acceptable to most regulators.

South Coast Air Quality Management District (SCAQMD)

The South Coast Air Quality Management District (SCAQMD) of southern California posts their BACT decisions online and is a good resource to use to identify control technologies applicable to the emission unit, or similar emission units. Simply follow the above link to their website and search through the BACT decisions.

SCAQMD BACT Database Search Result

In this example, the emission unit (or process) is a system for manufacturing fiber-impregnated material. The control technology that was considered BACT in this case was a baghouse for the control of particulate emissions from the process coupled with the use of zero-VOC materials.

Bay Area Air Quality Management District (BAAQMD)

BAAQMD BACT Workbook Search Result

The identification of applicable control technologies is often a difficult and time consuming task. The reason for this is that, in many cases, the expectations of the regulator go beyond simple online database and resource searches. If you are required to perform a BACT Analysis, I suggest you discuss available resources with your permitting engineer because in most cases they will be the one accepting or denying your analysis.

If you would like assistance with completing your BACT Analysis, I have the project experience and proprietary tools that make the process as quick and seamless as possible. Please feel free to contact me at any time for a FREE BACT Analysis Consultation.

The BACT Analysis requirement is common for the utility industry (e.g., a turbine at an electrical generating facility). Here are a few more uncommon cases where a BACT Analysis was required:

Tub-Grinder with 325-HP Diesel Engine

This Tub-Grinder, used to grind municipal waste at a landfill,
was subject to a BACT Analysis because of its potential 
emissions of nitrogen oxides (NOx).

Fuel Cell Test Stand

 Fuel cell test stands requiring a BACT Analysis for their potential
hydrogen emissions.
www.eutech-scientific.de

 It is important to consider all applicable regulations when determining whether or not you must perform a BACT Analysis. Again, the requirement is not dependant upon the process or equipment, but the type and amount of pollutant being emitted from the process or equipment. If you require assistance determining whether or not your project is subject to a BACT Analysis, or you need help with the BACT Analysis process, click here.

Natural Gas Fired Boiler

The BACT Requirement applies to new sources, or modifications of existing sources, which emit the following NSR pollutants:

• Pollutants with a National Ambient Air Quality Standards (NAAQS), also known as criteria pollutants, which include:
  • Ozone
  • Carbon Monoxide
  • Particulate Matter
  • Sulfur Dioxide
  • Lead
  • Nitrogen Oxide
• Other pollutants including sulfuric acid mist, hydrogen sulfide, etc.
• Note that some states, such as Connecticut require BACT for ANY pollutant

The federal regulations require that “Major Sources” and “Major Modifications to existing sources” perform a BACT Analysis. However, some states have more stringent requirements. The following are a few examples:

• Connecticut
  • Potential emissions greater than the threshold for major sources and major modifications
  • Potential emissions greater than 15-tons per year from ANY new emission unit or modification to existing emission units (not just major sources)
• South Carolina
  • Any new construction when the net VOC emissions increase is greater than 100-tons per year

For your state’s specific BACT requirements, you should check with your local regulator (City, County, State).

• Identify all available control systems that have the PRACTICAL POTENTIAL for application to the unit
• Eliminate TECHNICALLY INFEASIBLE systems
• Consider Energy, Economic, and Environmental Impacts
• Reject systems based on the above considerations

Those systems which are considered technically feasible are ranked from those providing the most control to those providing the least control. The emission rate utilizing the most efficient control system is considered the Lowest Achievable Emission Rate (LAER). For example, for the control of nitrogen oxides from a boiler a Selective Catalytic Reduction (SCR) system may provide the highest control efficiency while a Selective Non-Catalytic Reduction (SNCR) system may provide the least. In this case, the SCR would be ranked first and the emission rate associated with the use of the SCR would be the LAER.

In some cases, the control device providing LAER isn’t a feasible solution for pollution reduction from the emission unit. In general, energy, economic, and environmental impacts must be considered when determining a systems feasibility. Control scenarios are eliminated based on these impacts and the most efficient remaining system is the Best Available Control Technology or BACT.