Boiler technology |
Converting to natural gas: a new use for coal assets
Many coal fired power plant steam generators designed and supplied in the latter part of the twentieth century still have a remaining useful life. While coal – which is the fuel around which these units were designed and sets the performance of the plant – has come under increased scrutiny as the world looks to reduce greenhouse gas emissions, the need for reliable, baseload power continues to grow. It makes sense to find environmentally friendly ways to increase the life of these historically coal fired generation assets
John Koslosky Senior Director, Business Development, Thermal Projects, Babcock & Wilcox
Fuel switching to natural gas is increasingly being considered as a smart alternative fuel choice for coal fired plants. Whether the whole plant is converted to burn natural gas, or just part of the plant, there are a number of economic, regulatory, performance, emissions, fuel availability and cost considerations that plant owners and operators should weigh to determine the best solution for their plant and circumstances.
Project drivers – why consider a coal to natural gas conversion? Regulatory and economic considerations are two of the most-notable drivers in the decision to convert a steam generator from coal to natural gas firing.
A range of technology options for coal to gas boiler conversions
emissions from the unit, but also typically lowers other air emissions, including particulates, NOx
, SO2 and VOCs, and eliminates both effluents
Regulations vary widely across the globe and may be driven by international agreements or national, regional or local jurisdictions. Many coal-fired power plants have been slated for decommissioning, and these decisions are often made under the umbrella of reduced carbon dioxide, and other emissions, and effluent regulatory constraints. However, natural gas has been considered as a fossil fuel alternative to coal, offering the potential to utilise the remaining life of some generating assets, while providing fuel flexibility in the electricity generation mix. A coal to natural gas conversion not only lowers the CO2
from coal flue gas treatment and the need for ash treatment and storage.
The economics of a coal to natural gas conversion is another important consideration. In certain circumstances, the plant operator may find that the conversion makes economic sense, even if regulatory demands are not necessitating the fuel switch. Even with a regulatory need, economic considerations also must be understood, including the expense of bringing an adequate and consistent supply of natural gas to the site and the expected future cost of the fuel versus coal. In addition to fuel costs, natural gas will be of economic benefit as certain environmental controls for sulphur and particulates can be eliminated (as natural gas emits no significant levels of these pollutants). Also, natural gas has inherently lower costs of operation and maintenance, as certain parts of the plant such as coal yards and pulverisers are eliminated, and ongoing wear is minimised as the effects of corrosion and erosion on plant equipment are eliminated.
Fuel availability Retractable wall-fired gas igniter
The first consideration in determining whether a coal to natural gas conversion is feasible is the availability of natural gas to the site, or the expense of building a reliable and adequate natural gas supply to the site. In the 21st century, investments in natural gas exploration and supply technology and infrastructure have made reliable and low-cost natural gas supplies readily available in many parts of the globe.
B&W XCL-S® low-NOx burner Gas fuel train
In locations where a reliable and low cost natural gas supply is, or can reasonably be, available, the economics of natural gas firing can be favourable in comparison to clean coal. In making these comparisons, it’s important to factor in not only the coal and natural gas fuel costs, but also the operation and maintenance expenses of the facility, which are notably lower when firing natural gas.
Furnace gas recirculation
Dual fuel hydrogen and natural gas burner
Efficiency and economics While the firing of natural gas lowers steam generator efficiency in comparison to most coals, the negative impact on plant heat rate can be fully or partially offset by the elimination of equipment utilised in coal firing that consumes parasitic power.
12 | October 2024|
www.modernpowersystems.com
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