High BTU Gas Plant - Landfill Gas, Coal Beds, and Digesters…
We get a lot of questions about landfill gas (LFG). What exactly is it? What can you do with it? Can my boiler use it? Do I have to clean it before I can use it? Should I make High BTU gas or Electricity with it? And so on, and so on.
The following are Venture Engineering’s insights about LFG, what we’ve been doing with it, the types of systems we’ve engineered, and for all those developers and/or engineers out there that rely so heavily on rules of thumb, we have those too.
Years ago, landfill operators recognized the opportunity for energy recovery from landfill gas (LFG). Starting about the early to mid 1980’s landfill operators began to collect and capture the landfill gas and began producing electricity with it. And this was done well in advance of the NSPS requirements to collect and control methane from landfills. Landfill gas, in general, consists of about 50% methane and 45% carbon dioxide, 2-3% nitrogen, 0.5% oxygen, and 1.5%-2.5% others (usually non-methane organic carbon constituents called NMOCs). As such, it has about half the heat content of natural gas. In those early days, LFG was converted to electricity using mostly internal combustion engines and generators (i.e., IC engine gensets). Because of the gas properties and the IC engine technologies that existed then, it took about 600 cfm of LFG to produce 1 MW of power. Today, after some 25 years of engine development, a good current rule of thumb is 1MW of power from 400 cfm of landfill gas.
Subsequently, and especially in the current energy market, there are attractive alternatives to on-site electric generation. Today’s technologies allow for methane recovery and the economic production of high Btu gas which can be prepared to meet the most stringent of natural gas fuel specifications and delivered into local natural gas pipelines for sale to end users. Such fuel production strategies deliver to the landfill operator valuable revenues as well as recognition of environmental stewardship.
Venture and its staff have been involved in a number of LFG to energy projects, including LFG to electricity using both IC engine as well as turbines, LFG to high BTU using pressure swing adsorption and membranes, and landfill gas to boiler (direct use medium BTU application). While there are other technologies available to produce high BTU gas (i.e., amine solvent extraction, etc.), only the PSA and membrane technologies are attractive in most cases.
Additionally, Venture has found that a high BTU gas project can often offer greater value than a LFG-to-electricity project. In areas where there is a low spark spread, which is the difference between the cost of fuel required to produce electricity and the price of that same unit of electricity, a high BTU gas project may be economically viable where a power plant would not. High BTU gas projects offer many distinct advantages over an on-site electric generation project. These include:
- Shorter development time, allowing for quicker returns on capital. Venture can realize a high BTU gas plant within 12 months of a notice to proceed compared to 18 to 24 months for a power project. (using 100% modularized PSA process described in more detail below)
- Delivering the gas into a nearby pipeline for distribution so that electric generation can be maximized off-site, utilizing a high efficiency combined cycle power plant.
- Lower noise levels and emissions than an electric generation plant, thereby creating greater community support.
- Less permit requirements due to negligible air emissions.
- Modular units can be easily moved and assembled. Allows for ease in future expansion as LFG flows increase.
LFG has been successfully processed into High BTU gas at various facilities in the US for over 20 years. At one time, only very large sites were commercially feasible for processing LFG into pipeline quality gas. Prior to recent developments and improvements in technology, a good rule of thumb was around 3,000 to 4,000 cfm (inlet) to be economically feasible. Processing LFG at much smaller volumes is now possible given the current gas economics, improvements in processing technology, and a modularized approach. In fact, it is now feasible for processing LFG into high BTU gas with as little as 1,000 cfm of LFG (and as low as 300 cfm for anaerobic digester gas!)
Further, Venture believes that the most economical LFG to high BTU gas process is done via Pressure Swing Adsorption. Venture has developed a completely modularized high BTU gas plant, using several industry proven components. The heart of the process includes QuestAir Technologies, Inc. patented PSA process. A typical LFG to high BTU gas plant includes gas conditioning skids (drying, sulfur and siloxanes removal), followed by compression, pressure swing adsorption, and a flare/TOU for off-gas control. Depending on site specific conditions and gas analysis, a standard 2,500 cfm system capable of producing high BTU pipeline quality gas with a 90% recovery efficiency (i.e., a 2500-90), can be implemented in under 12 months for as little as $5.5M. Standard modularized plant sizes include 2000-90, 2500-90, and 4000-90. Additionally, if higher recovery efficiencies are economically feasible, a second stage PSA can be added to any of the standard ‘90’ packages that would increase the recovery to as much as 96%.
Furthermore, this same technology has been readily applied on anaerobic digester gas (biogas) and coal bed methane. The only real differences between the applications are the upfront gas conditioning requirements (typically less complex for digester and coal bed methane)
To learn more about Venture Engineering & Construction’s capabilities with respect to landfill gas processing, please contact Mr. Bill Slatosky at 412-231-5890, or email at bslatosky@ventureengr.com.