NEWS RELEASE                                                                                                    APRIL 2015

Difficult Complex Decisions For Coal-fired Power Plant Operators

Changing fuel prices, government regulations and technology all combine to make decision making difficult for operators and developers of coal-fired power generation facilities around the world.

Power plant designers in developing countries face new local environmental regulations plus additional requirements stipulated by lenders such as the World Bank.  In the developed world, the regulations keep getting tougher. So operators must not only deal with the current round of upgrades but the next round as well.

Recent extreme changes in the price of oil and gas need to be factored into decisions. The price and availability of coal needs to be forecast. The option to burn gas in an existing coal-fired boiler or to retire the boiler and replace it with a more efficient gas turbine combined cycle power plant is relevant for older coal-fired power plants subject to expensive environmental upgrades.

The most difficult challenge is to keep up with all the new technology options.  Stringent mercury regulations have resulted in the following choices:

  • Activated carbon injection ahead of the existing precipitator
  • Activated carbon injection ahead of a new fabric filter
  • Non-carbon sorbents
  • Halogen addition to the fuel and capture of oxidized mercury in the scrubber
  • SCR catalyst with higher conversion rate of elemental mercury to the oxidized form
  • Post scrubber non-regenerative  mercury capture module
  • Mercury CEMS or sorbent traps
  • Use of mercury CEMS for double duty including compliance and process control (other option is a 2nd CEMS)

The technology to capture SO2 has constantly expanded and improved since the first commercial installation in 1968 at Union Electric in St Louis.  Options now include:

  • Limestone spray tower or tray tower
  • Lime scrubbing with smaller scrubber size and flow
  • Spray drier with lime slurry
  • Spray drier with lime slurry and direct sorbent injection upstream for higher efficiency
  • Circulating dry scrubbers (CDS) with either fluid bed (CFB) or gas suspension absorber (GSA)
  • Direct sorbent injection (DSI) with sodium,  lime or even finely powered limestone
  • Adsorption on activated carbon and sulfuric acid generation
  • Absorption with ammonia and fertilizer production
  • Absorption with amines and sulfur production
  • Catalytic conversion of SO2 and production of sulfur products
  • Hot gas catalytic filter with DSI with either high surface area hydrate or finely ground limestone injected in the furnace or both

The requirements for particulate removal are more stringent everywhere. In Russia, China, South Africa, the U.S. and many other countries existing precipitators are going to be upgraded or replaced to meet limits as low as 5 mg/Nm3.  Options include:

  • New larger precipitator
  • Hybrid with one field replaced with bags
  • Complete retrofit of precipitator shell with bags
  • New fabric filter for 350oF
  • New 850oF ceramic fabric filter with more efficient heat exchanger for improved boiler efficiency
  • Wet precipitator with initial capture in baghouse or dry precipitator
  • Wet precipitator with only a venturi scrubber ahead of it for particulate control and SO2 capture

NOx control options include:

  • Low NOx burners
  • Combustion modifications
  • Selective catalytic reduction (SCR)
  • Selective non-catalytic reduction (SNCR)
  • Ozone
  • Hydrogen Peroxide
  • Various combinations of the above and various control locations e.g. tail end SCR after the scrubber

The power plant decision maker has to keep moving back and forth among decision trees as he makes the above decisions. Some limit fuel selection. Some present solid waste problems. Some contribute to water pollution problems.

This complex set of tasks has been organized into a system: 44I Power Plant Air Quality Decisions.  This system is free of charge to any of the world’s power plant operators and by yearly subscription to others. The operating system is the 4As.  This includes Alerts, Answers, Analysis and Advancement.  The answers are contained in a Decision Orchard.  The complex navigation is greatly simplified by Global Decisions Positioning Systems™ (GdPS).  Here are two examples:

        SO3 Fast Track Global Decisions Positioning System™ (GdPS)

        Hot Gas Filtration Global Decisions Positioning System™ (GdPS)