A modern power plant featuring large cooling towers and a blue facade. Power lines run in the foreground.
RWE Innovation Centre – Reducing mercury emissions using lignite coke

Reducing mercury emissions using lignite coke (HOK®, German: Herdofenkoks)

Two versions of process: “dry” in continuous operation/ “wet”

The technology for mercury emission reduction which is in operation today has been tested in a demonstration unit in Niederaussem before.

  • The purpose of the demonstration system was to refine and perform long-term testing of innovative versions of procedures to reduce mercury emissions in flue gas from lignite/coal-fired power stations using lignite coke (HOK®) in continuous, automated operation
  • Full-scale system at a flue gas train at the BoA1 lignite power station in Niederaussem, volumetric flow of flue gas approx. 1.6 m3N/h
  • HOK® supply for “wet” and “dry” versions from shared silo container
  • Expansion of mercury system to supply both flue gas trains at BoA1 in subsequent commercial operation
  • Project executed by the technical services of RWE Power and RWE Technology International
  • Contractor: ISS Schüttguttechnik GmbH
  • Demonstration operation since beginning of 2019

Dry version includes:

  • Dosing and simultaneous distribution to 16 nozzles via pneumatic delivery lines
  • Delivery supply and compressed air supply
  • Variation of injection speed for optimum penetration depth and even distribution of HOK®

Wet version includes:

  • HOK® mixture with water and wet grinding in a stirred media mill
  • Buffer container, reservoir and loop line system to 16 nozzles
  • Variation in particle size

R&D programme by RWE to reduce mercury emissions

Optimising of all power stations, but with focus on lignite

  • Market overview: Mercury reduction

    • Literature search
    • Talks with manufacturers
    • Feasibility studies

  • High-performance scrubber

    • HOK injection, dry/wet
    • Test of various adsorbents, flue gas, REA
    • Flue gas 30,000 m3N/h
    • Lignite, BoA1

  • Mercury reduction in hard coal

    • GKM, EnBW, RWEP, University of Stuttgart

  • Trials at DE2, Berrenrath

    • HOK injection, dry (existing)
    • Proof of Concept for wet injection
    • Flue gas 400,000 m3N/h
    • Lignite, sewage sludge 

    VGB Project GORE Mercury Control

    • Uniper, LEAG, EnBW, RWEP, Dresden University of Technology

  • Pilot mercury plant, BoA1

    • HOK injection, wet
    • Wet grinding
    • One full-scale flue gas train
    • Flue gas 1,600,000 m3N/h
    • Lignite

  • Mercury demonstration system, HgA BoA1

    • Mercury demonstration system, HgA BoA1
    • HOK injection, dry/wet
    • Automatic
    • One full-scale flue gas train
    • Flue gas 1,600,000 m3N/h
    • Lignite

    Commercial mercury capture

    • Choice of technology
    • Planning
    • Approval

  • Commercial mercury capture

    • Construction
    • Commissioning
    • Operation

    Commercial mercury system, BoA1

    • Choice of technology
    • Installation on 2nd flue gas train
    • Operation

What is HOK®?

  • Lignite coke or activated coke (HOK®) is produced from Rhenish lignite using the hearth refining process.
  • HOK® has a large specific surface area and a favourable pore radius distribution, with a large proportion of mesopores and macropores.
  • The pore diameter of 1 to > 50 nm enables easy access to the inner surface.

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