The Evolving Mercury Abatement Market
Due to the increasingly stringent EPA regulation on mercury and the many variables surrounding in-duct capture technology, the mercury abatement market continues to change and grow. Injecting powdered activated carbon into flue gases is showing proven results in meeting the increasing compliance standards for mercury abatement.
But because the EPA standards regulate emissions on many pollutants, technology must be able to handle activated carbon injection (ACI) and a combination of other non-carbon designer sorbents (e.g. amended silicates). These designer sorbents are being developed with finer particle sizes and unique chemistry so as to increase removal rates not only for mercury abatement, but for SO2, SO3, HCl, and HF as well. The physical material handling properties of the new sorbents impact the pneumatic conveying system design. ACI/sorbent injection rates are being increased to meet the newest compliance standards. There is also an increasing demand for longer conveying distances, so as to allow placement of multiple silos in one offloading location. Therefore, the ACI system must be designed properly to convey various sorbents, at increased injection rates over longer distances.
Nol-Tec has been working to meet these new challenges.
Ideally, power producers need a system that allows them to inject any sorbent they want, at whatever rate they want, through a system convey routing that they choose. And of course, reliability is critical to the success of meeting MATS.
Eductor technology has long been a standard in ACI technology. However, an eductor system will not perform reliably if the system pressure exceeds 3 PSI. Higher injection rates, longer conveying distances, and the use of designer sorbents will dictate that an alternative be utilized.
A viable alternative to the eductor design incorporates the use of a zero clearance rotary airlock (RAL) to meter product into the dilute pressure conveying system. The zero clearance RAL greatly improves the feeding of PAC due to reduced leakage. This technology provides a slight increase in system pressure capability, up to 6 PSI. However, this design is not entirely reliable at the top end of its pressure range. Some RAL leakage will still occur and material abrasion (especially with some designer sorbents) can reduce the life of the RAL.
By listening to customer needs, Nol-Tec Systems has designed and innovated a convey system which is able to meet the need to convey higher rates, longer distances, and different sorbent types. This pressurized continuous transport system provides the capability to meter material at system pressures up to 12 PSI. Nol-Tec’s Gen 3 systems meet the mercury abatement challenges our customers are facing. To further confirm we were meeting our customers needs, in 2013 Nol-Tec invested time and effort into field testing.
Mercury Abatement Trials
Utilizing a large fleet of portable, self-contained testing equipment, Nol-Tec ran tests on site of both power plants and industrial boilers, in real-world conditions. Most tests were for mercury compliance with MATS standards. However, EGUs and IBs also wanted to control SO3 emissions that are not directly included in MATS, but necessary nonetheless for enhanced Hg removal. Many tests included injecting both alkaline products and Hg sorbents. This helped us prove not only that Nol-Tec’s systems can produce the correct levels of mercury abatement, but also provide the flexibility our customers demand.
At multiple test sites, Nol-Tec proved again and again that our Gen 3 could meet the challenges presented by powder activated carbon (PAC) and mercury abatement standards. We used a variety of PAC formulations, as well as mixing different kinds of sorbents with PAC to meet requirements. We ran systems at higher injection rates than a standard eductor system could handle. We worked with fluctuating pressures (a reality in pneumatic conveying) and long convey distances. In every case, we were able to bring mercury and other pollutant levels into compliance with EPA standards, efficiently and effectively. PAC and activated carbon injection do work for mercury abatement when used with a correctly designed pneumatic convey system.
More test result details can be found in the August 2014 issue of Air Pollution Control Magazine or on our website under case studies.View All News