With new regulations limiting mercury and SO2 emissions due to come into force by 2021, executives at German power company Eins Energie in Sachsen (Saxony) knew it was time to make a change. Their coal-fired combined heat and power plant in Chemnitz (Figure 1) was not due to be shut down for at least ten years and they needed to meet the new standards as soon as possible in the existing plant.

Roland Warner, CEO of Eins, explains: “The heat supply in Chemnitz is still largely based on lignite coal today. This type of generation produces mercury that has to be disposed of. We needed a way to comply with regulations and continue to operate our coal units in an environmentally friendly manner until they are shut down – not before 2029.”

For the solution, the operators of the Chemnitz CHP plant turned to an innovative technology from W. L. Gore & Associates.

The GORE(TM) Mercury and SO2 Control System (GMCS) is a passive system for flue gas cleaning that is typically installed in the plant’s existing wet scrubber. The modules contain Gore’s proprietary sorbent polymer catalyst (SPC). It separates SO2 as well as elemental and oxidised Hg from industrial exhaust gases. SPC modules were installed at the Chemnitz site in August 2018 (Figure 2), a process that took just 18 days. They cut Hg emissions by half enabling the Chemnitz CHP to comply with the new limit values.

The GORE(TM) Mercury and SO2 Control System has already been proven for four years in various US coal-fired power plants. The Chemnitz combined heat and power plant is pioneering the technology in Germany. After various test installations at other locations, it is also the first commercial use of the GMCS in Europe. Due to the comparatively uncomplicated installation in existing plants, this technology could also be a tried and tested alternative for other coal-based power plants. 

“The UN’s efforts to reduce global mercury emissions are increasing European and national requirements for coal-fired power plants,” said Ole Petzoldt, business development manager at W. L. Gore & Associates GmbH. “Eins wants to do even more for the environment and its employees here in Saxony. Gore’s technology makes this possible. It eliminates the need to add chemical additives, for example, as is the case with conventional separation processes. The GMCS modules are designed for a service life of several years and do not require any additional ‘maintenance’ during this time. The GORE(TM) Mercury and SO2 Control System is an innovative solution that eliminates many of the undesirable complications and high operating costs associated with traditional mercury control systems. It can be a viable alternative, replacement, or complement to an existing system, providing decreased operating costs, increased compliance margin, and simplified plant operation.”

Fluoropolymer based

At the heart of the GMCS technology is the SPC composite, an innovative, fluoropolymer based material developed by scientists at Gore.

The sorbent in this material efficiently captures both elemental and oxidised mercury from the flue gas stream and is insensitive to fuel or process changes. Unlike with many activated carbon sorbents, the presence of SO3 does not inhibit mercury capture by the SPC. Since there are no injected sorbents or chemicals, there is no concern over fly ash contamination, halogen-induced corrosion, or wastewater treatment complications. The catalyst in the SPC converts SO2 to sulphuric acid, which is neutralised in the scrubber.

The SPC material is contained in discrete modules to form the GORE(TM) Mercury Control System. The modules are designed with an open channel structure (Figure 3), which provides extremely low pressure drop avoiding the need for an additional booster fan. A typical installation only adds 1.0 – 1.5 inches of water (250 to 373 Pa) pressure drop. Operation is passive; the modules will continuously capture mercury for many years without requiring any adjustment, regeneration, or replacement.

The GMCS can also serve as a barrier to mercury re-emissions from a wet flue gas desulfurisation system, eliminating the need for re-emissions additives.

The individual stackable modules can be stacked in as many layers as required to achieve the targeted emission levels for mercury and SO2.

When the modules have reached end of life, the SPC material can be removed from the metal frames for disposal. The quantity of SPC material that needs to be disposed of is typically several orders of magnitude less than the quantity of injected sorbents resulting in lower disposal costs.

Installation options

Installation of GMCS inside an existing wet scrubber (Figure 4) results in no additional footprint requirements.

Alternatively, modules may be installed in a horizontal flow orientation. This allows installation in the expanded outlet duct of a wet scrubber. In systems without an existing wet scrubber, the GMCS can actually provide the primary SO2 control depending on the actual SO2 removal needed. This is generally not applicable in Europe, but is gaining interest in other parts of the world where FGD technologies have not yet been broadly installed.

In the USA, the GORE(TM) Mercury Control System is currently in operation at a total of 2100 MW of coal fired power units and 18 sewage sludge incinerators.

Three demonstration plants have already been successfully executed in Europe: Belchatow, Poland; Patnow, Poland; and Schkopau, Germany.