Field Testing of Activated Carbon Injection Options for Mercury Control at TXU's Big Brown Station

Pavlish, John ; Thompson, Jeffrey ; Martin, Christopher ; Musich, Mark ; Hamre, Lucinda

University of North Dakota

关键词: Removal;    Powder River Basin;    Particulates;    Testing;    Activated Carbon;   

DOI  :  10.2172/945024
RP-ID  :  None
RP-ID  :  FC26-05NT42305
RP-ID  :  945024

美国|英语

来源: UNT Digital Library

【 摘 要 】

The primary objective of the project was to evaluate the long-term feasibility of using activated carbon injection (ACI) options to effectively reduce mercury emissions from Texas electric generation plants in which a blend of lignite and subbituminous coal is fired. Field testing of ACI options was performed on one-quarter of Unit 2 at TXU's Big Brown Steam Electric Station. Unit 2 has a design output of 600 MW and burns a blend of 70% Texas Gulf Coast lignite and 30% subbituminous Powder River Basin coal. Big Brown employs a COHPAC configuration, i.e., high air-to-cloth baghouses following cold-side electrostatic precipitators (ESPs), for particulate control. When sorbent injection is added between the ESP and the baghouse, the combined technology is referred to as TOXECON{trademark} and is patented by the Electric Power Research Institute in the United States. Key benefits of the TOXECON configuration include better mass transfer characteristics of a fabric filter compared to an ESP for mercury capture and contamination of only a small percentage of the fly ash with AC. The field testing consisted of a baseline sampling period, a parametric screening of three sorbent injection options, and a month long test with a single mercury control technology. During the baseline sampling, native mercury removal was observed to be less than 10%. Parametric testing was conducted for three sorbent injection options: injection of standard AC alone; injection of an EERC sorbent enhancement additive, SEA4, with ACI; and injection of an EERC enhanced AC. Injection rates were determined for all of the options to achieve the minimum target of 55% mercury removal as well as for higher removals approaching 90%. Some of the higher injection rates were not sustainable because of increased differential pressure across the test baghouse module. After completion of the parametric testing, a month long test was conducted using the enhanced AC at a nominal rate of 1.5 lb/Macf. During the time that enhanced AC was injected, the average mercury removal for the month long test was approximately 74% across the test baghouse module. ACI was interrupted frequently during the month long test because the test baghouse module was bypassed frequently to relieve differential pressure. The high air-to-cloth ratio of operations at this unit results in significant differential pressure, and thus there was little operating margin before encountering differential pressure limits, especially at high loads. This limited the use of sorbent injection as the added material contributes to the overall differential pressure. This finding limits sustainable injection of AC without appropriate modifications to the plant or its operations. Handling and storage issues were observed for the TOXECON ash-AC mixture. Malfunctioning equipment led to baghouse dust hopper plugging, and storage of the stagnant material at flue gas temperatures resulted in self-heating and ignition of the AC in the ash. In the hoppers that worked properly, no such problems were reported. Economics of mercury control at Big Brown were estimated for as-tested scenarios and scenarios incorporating changes to allow sustainable operation. This project was funded under the U.S. Department of Energy National Energy Technology Laboratory project entitled 'Large-Scale Mercury Control Technology Field Testing Program--Phase II'.