Waste to Energy Menu
What is Landfill Gas?
Landfill gas (LFG) is generated during the natural process of decomposition of organic material contained in solid waste landfills. It’s a composition of about 50 percent methane and 50 percent carbon dioxide and water vapor. In addition, it also contains small amounts of nitrogen, oxygen, and hydrogen, less than 1 percent nonmethane organic compounds (NMOCs), and trace amounts of inorganic compounds.
Leader in Landfill Gas Treatment
Venture Engineering and Construction provides its customers with profitable solutions for their landfill gas. Not just in the process of converting landfill gas to energy, but also with a proprietary gas conditioning system that significantly decreases down time, increases efficiency, reduces maintenance costs, and easily meets emission standards. Venture’s engineering team is comprised of highly skilled professionals who can evaluate your needs, design a project that will maintain environmental compliance and provide you with a new source of revenue.
Our team is highly experienced in developing direct use projects, electric generation, pipeline quality gas from landfills and all leading technologies utilized in the landfill gas industry.
Venture assumes responsibility for the specialized engineering, design, procurement, construction, installation, commissioning, and operation and maintenance of the energy system.
Benefits of Landfill Gas
Landfill gas projects generate revenue from the sale of the gas and also create green jobs associated with the design, construction, and operation of energy systems. Once converted, landfill gas can be utilized in many ways: to generate electricity, heat, or steam; as an alternative vehicle fuel; or sold on the energy market as a renewable “green” power or gas.
- Electricity is the most widely used of the landfill gas projects. The electricity can be used for internal facilities or sold to external consumers.
- Direct-Use is used to replace non-renewable resources such as coal, oil, and natural gas.
- Cogeneration produces both electricity and thermal energy. This normally relates to steam or hot water and is very efficient.
- Pipeline Gas is a high Btu application. Landfill methane is processed to meet interstate pipeline standards and is injected into the delivery system. High value Btu systems generate premium value for landfills.
High BTU Gas Processing (Landfill Gas to Energy)
The following section provides a general overview of the unit operations found at high BTU gas plants.
Hydrogen Sulfide Removal
There are a variety of commercially proven processes available to remove H2S from gas streams. These processes can be divided into wet and dry processes. The dry processes are generally non-regenerable and are characterized by having low capital costs but high relative operating costs ($/lb. of H2S removed). Wet processes are just the opposite in that they are usually regenerable but have high capital costs and low relative operating costs. Based on Venture’s previous assessments, the point at which the economics switch from the dry systems to the wet systems is usually around 300 pounds of H2S/day.
The oldest dry system still in use today is the iron sponge process, which consists of wood chips impregnated with hydrated ferric oxide. The H2S reacts with the ferric oxide to form iron sulfide. The spent media can be regenerated by passing air through the bed, which converts the iron sulfide back to ferric oxide and elemental sulfur. This process has been successfully employed for many years on landfill gas; however, it has lost some appeal due to the environmental and safety problems associated with handling and disposing of the spent media.
Another dry system that has been successfully employed on landfill gas consists of an iron oxide impregnated on a ceramic base. As the H2S passes over the media it reacts with the iron oxide to form innocuous iron pyrite. The process is not regenerable, but it is attractive because the safety problems associated with iron sponge are eliminated. The two commercial processes employing this technology are Sulfur-Rite® and SulfaTreat®.
Activated carbon can also be employed for selectively removing H2S from landfill gas; however the high cost of replacing and disposing of the carbon generally limits its use to polishing applications (very small amounts of H2S to be removed).
There are several wet systems available for selectively removing H2S from landfill gas in one step, including wet scrubbing, the LO-CAT® process, and the Thiopaq process.
All of the above processes are capable of removing 99.9+% of the H2S and have been proven in landfill gas service for several years.
Moisture removal is always required at a LFG processing facility, whether making electricity or high BTU gas. Condensate forms when warm gas from the landfill cools as it travels through the collection system and after compression. If condensate is not removed, it can block the collection system and disrupt the energy recovery process and lead to the formation of corrosive compounds.
After the LFG has been collected and before it can be used in a conversion process, it must be treated to remove condensate not captured in the condensate removal systems, particulates, and other impurities. Moisture removal is often classified as primary and secondary treatment. Primary moisture removal, or dewatering, includes physical removal of free water or condensate in the LFG via knockout devices such as knockout pots and coalescing filters. Secondary treatment includes chilling, drying and compression.
Pipeline gas specifications require moisture to be < 7 lb per million cubic feet (MCF). As such, all high BTU gas projects need primary and secondary moisture removal. Secondary moisture removal often includes removal of water vapor or humidity in the LFG by using gas cooling/chilling or desiccant drying, followed by compression. Typical chiller/cooling dew points are 40°F, while desiccant drying can achieve dew points approaching -80°F.
When considering moisture removal technology, it is important to consider the CO2 removal technology. The CO2 removal technology may impact the moisture removal efficiency of a high BTU gas plant.
NMOC Removal & Siloxane Removal
Non-methane organic compounds (NMOC’s) and Siloxanes must be removed as both are contaminants that are regulated by pipeline specifications.
In order to achieve and maintain the concentration standards for each COC, advanced gas cleaning will be required. Most likely, the gas cleaning technology will involve both regenerable siloxane removal as well as regenerable activated carbon.
These regenerable gas cleaning systems would be regenerated with inert tail gas from the CO2 removal technology. Venture envisions that this tail gas would be heated with waste heat from the new TOU that would be equipped with a waste heat exchanger.
Carbon Dioxide Removal
Carbon dioxide removal is the heart of the high BTU gas plant. Generally speaking, there are only three CO2 removal processes being used on biogas:
- Solvent Extraction (Selexol & Kryosol)
- Pressure Swing Adsorption (PSA)
- Membrane Separation
To date, every commercial scale high BTU gas plant uses one of these three CO2 removal technologies (or a combination of them). The following table represents the list of known high BTU gas plants (and their associated CO2 removal technology), currently operating in the U.S.