Volume 3, Number 1
A Gossman Consulting, Inc. Publication
January 1997

This month's GCI Tech Notes is the third in an intermittent series of comments on selected aspects of the proposed EPA Hazardous Waste Combustor Rule. Contributions were made by the entire GCI Staff.

Hazardous Waste Combustor Review - Chapter 3 Alternative to CO/HC Monitoring for Maintenance of Good Combustion Conditions in Cement Kilns

The EPA has presented the monitoring of total CO and hydrocarbons in cement kiln stacks as a necessary requirement to demonstrate combustion efficiency of hazardous waste fuels in cement kilns. This also supposedly limits the production of products of incomplete combustion (PICs). Indeed, BIF was specific regarding the use of CO and HC monitoring and limits on their emissions as a method to demonstrate "good combustion" irrespec-tive of the subsequent emissions of hydrocarbons from the raw feed (Preamble to BIF Part 3, II, B and Part 3, II, B, 4). In the preamble to BIF, EPA states that the CO and HC limits are not health based, but "a measure of combustion efficiency."

The proposed HWC regulation retains HC limits as a method of demonstrating "good combustion", but states that the "HC levels resulting from organics in the raw materials can range from 10-400 ppmv. This makes it problematic to use HC as the only or the principal means to ensure good combustion efficiency of hazardous waste fuels to minimize emissions of toxic PICs (i.e., non-D/F organic HAPs)." (FR17397) Erroneously, in the proposed HWC regulations, EPA implies that BIF requires wet and long dry kilns, in order to meet the BIF standards, to "control the organics in raw materials coupled with operating under good combustion practices" (FR17397) while explicitly stating that for kilns with "by-passes" such a main stack HC emission limit is not required. So clearly, EPA intends the HC emission monitoring and emission limits purely to demonstrate "good combustion." Surely the EPA, if given a more reliable or alternative method of monitoring "good combustion" in cement kilns, would be forced by its own rules and stated concerns to seriously consider such a method.

Gossman Consulting, Inc. (GCI) believes that there are alternatives to utilizing HC/CO and that EPA should modify the proposed rule to allow any such alternatives demonstrated as viable by the industry. Good combustion is frequently referred to as the three Ts and O; or time at temperature, temperature, turbulence and excess oxygen. We believe that one example of a technically sound alternative that could be developed would be the continuous or semi-continuous monitoring of the destruction and removal efficiency (DRE) of SF6. Such a system should provide excellent monitoring to insure adequate temperature, time at temperature and turbulence are present since SF6 is a proven temperature liable POHC. Maintaining excess oxygen using kiln exit O2 or a sudden excursion of CO could complete the picture. Setting a CO limit during stack PIC testing may be another alternative.

In reviewing this option, GCI has determined that a system for continuously (a reading every one to four minutes) monitoring SF6 DRE can likely be installed for approximately $100,000 and annual operating costs should be $100,000. Thus SF6 DRE monitoring presents an option that would appear to be financially viable. We would also note that continuous monitoring of SF6 DRE should eliminate the need to directly (This is impossible anyway.) monitor combustion zone gas temperatures. GCI also believes that continuous monitoring of SF6 DRE with an appropriately designed AWFCO should enhance the confidence from the public and community relative to the issue of maintaining good combustion conditions.

GCI has strongly urged the agency to research and consider alternatives to HC/CO as an indicator of good combustion conditions in a cement kiln. We believe that the agency has not demonstrated and has indeed acknowledged that this requirement is inappropriate for some cement kilns. Industry should be encouraged to develop alternatives via appropriate additions to the language of the proposed regulations. Furthermore, we believe that the combination of SF 6 DRE and CO/O2 monitoring of some type may have superior characteristics for assuring that proper combustion zone conditions are maintained.

As used in the HWC regulation, the pursuit of Good Combustion is a confusing concept. Especially since the major justification for these operating parameter limits is to control dioxin/furan emissions - even though the connection between these emissions and the parameters are not distinctly direct. The concept of Good Combustion for cement kilns is most especially confusing. As long as there are carogins in a kiln raw feed it is difficult to justify stack CO and HC concentrations as control parameters for good combustion or to control dioxins/furans. Also, the EPA has proposed some rather stringent operating limits on containerized waste combustion (including non-hazardous waste materials such as tires). EPA continues to confuse issues involving good combustion in incinerators and cement kilns. These devices have very different "good combustion" conditions.

BIF Requirement HWC Requirement
O2 CEM - required to standardize CEM values to 7% O2. Retained - with minor change in conversion of CO & HC concentration to 7% O2 for kilns with O2 level >7%.
CO CEM limit established in COC as max. HRA during runs. Retained:

- for main stack no limit

- for bypass duct <100 ppmv HRA @ 7% O2 (dry).*

HC CEM not required if CO is:

- <100 ppmv HRA @ 7% O2,

- otherwise HC must be <20 ppmv propane HRA @ 7% O2.

HC CEM required for:

- main stack must <20 ppmv (propane) HRA @ 7% O2 (dry),*

- bypass duct must be <6.7 ppmv (propane) HRA @ 7% O2 (dry).*

* For bypass duct, the CO limit or the HC limit applies, not both.

Facility may monitor bypass duct instead of main stack. Retained - however, there are different limits. (See above)
Minimum Combustion Zone Temperature Retained with substantial changes in wording of probe location.
Maximum flue gas flow rate.

- In BIF, this was included mainly as a limit to protect the operating integrity of the APCD. Established during the metals runs of the COC test. Maximum HRA of a flow indication (e.g. I.D Fan RPM)

Maximum flue gas flow rate set in performance test as the average of the maximum HRA for each run.

Maximum production rate. Set in performance test as the average of maximum HRA for each run.

Maximum waste fuel feed rate.

- total hazardous waste fuel feed rate set during COC test as an average maximum HRA of each run.

- Pumpable hazardous waste fuel feed rate set during COC test as an average of maximum HRA of each run.

Retained as maximum total waste fuel feed rate. There is no distinction regarding liquid waste fuel feedrates. Also, each hazardous waste feed point (at different locations) is considered separately, (i.e. hot end, mid-kiln, cold end).
Containerized hazardous waste fuel feed rate. Calculated as part of the total waste fuel feed rate. COC test had to include this method of feeding to allow use of this method. Note: Includes containerized non-hazardous waste such as tires.

- Feed rate limits are as noted above.

- Limits container mass to lightest injected during performance test.

- Limits interval between containers to longest period during performance test.

- Limits minimum oxygen to maximum instantaneous oxygen during performance test.