Underground coal mines produce a large amount of methane. Much of this methane gets trapped in the mine shafts with the miners, making it a very dangerous, and potentially explosive work environment. To reduce the amount of methane in the mine with the miners, vents are used to sypher the methane out, while bringing fresh air in. This exhaust of methane into the atmosphere is called Ventilation Air Methane, or VAM. VAM is responsibly for roughly 70% of all coal mine methane emissions, and while generally considered too diluted to be explosive, this methane presents an environmental risk, as well as a source of lost revenue.
A Ventilation Air Methane Thermal Oxidizer (VAMTOX), or CH4 Regenerative Thermal Oxidizer, is a specialized type of the thermal oxidizer, designed to handle methane (CH4) produced by many applications, including mining, industrial, and municipal waste streams. Methane (CH4) is a hydrocarbon, that consists of a single carbon atom and four hydrogen atoms. It is considered a greenhouse gas and a known contributor to climate change. It can also be incredibly dangerous in an industrial setting because it is highly explosive and exposure to methane gas can result in several serious physical issues. The extreme risks associated with methane are why governments have started requiring the use of VAM RTOs in mining operations. Coal Mine vent shafts emit many tons of methane each year. Carbon credit programs to incentivize methane destruction rather than venting are set to begin in 2021 under the current emissions trading system (ETS).
The first part of a VAM plant is a VAM Regenerative Thermal Oxidizer, or CH4 RTO. This type of oxidizer uses extremely high heat to clean the exhaust of dangerous pollutants, such as methane, created by coal mines. Developed for large volumes and varying Volatile Organic Compound (VOC) concentration air pollution applications, this technology is perfectly designed to meet the needs of coal mines.
An RTO works through a 2-step process:
Step 1: The RTO unit is brought up to combustion temperature using supplemental fuel such as natural gas, propane, diesel, or bio-fuel. During this start up period the RTO unit initially purges itself with fresh air and continues to process fresh air until it reaches combustion temperature equilibrium. The RTO unit is now ready to switch over to process air and begin the thermal oxidation of VOCs with destruction removal efficiency (DRE) up to 99.5%.
Step 2: The RTO switches from start-up mode running on clean air to operating on VOC process air from the source. To maximize heat recovery, the RTO will automatically cycle or alternate the inlet and outlet (see diagrams below) via a series of pneumatic, hydraulic, or electric valves.
What sets a VAM RTO apart from a traditional RTO?
If the Methane concentration is greater than 0.25%:
- RTO self-sustaining
- Excess heat
- Hot gas bypassed to boiler
- Boiler generates steam
- Steam runs turbine generator
Because the RTO is so efficient at reclaiming effluent heat, the units often times are capable of sustaining combustion temperatures without any supplemental fuel, utilizing the VOC steam as the only source of fuel. This technology is highly desirable because it is self-sustaining and offers up to 99.5% destruction rate efficiency.
Waste-to-Power (WTP) System Overview – 5-Step Process
- Waste Collection
A well-functioning WTP system includes a process operation in close-proximity to the power generation unit. Mining, industrial, and municipal waste streams are delivered to the processing facility site so that there is always consistent source at the site to minimize downtime.
- Process Waste Conversion
The first stage is to process the waste steam in a Regenerative Thermal Oxidizer generating the waste heat required for recovery and beneficial use. The oxidized gases are sent through the waste heat boiler for generating steam in order to provide steam to the steam turbine generator.
- Steam Generation
The Heat Recovery Steam Generator, or HRSG, utilizes the hot gas from the thermal oxidizer to produce steam. The first state in the HRSG is what is referred to as a water tube type heat recovery unit. This refers to the process fluid, such as the steam or water being on the inside of the tube with the products of combustion being on the outside of the tube. The products of combustion are normally at or close to atmospheric pressure, therefore, the shell side is generally not considered to be a pressure vessel.
- Power Generation
The steam that is generated in the HRSG is the motive force for electricity generation in the steam turbine. The power generation portion of the system is a turbine generator (TG) set for on-site power and distributed energy and typically are sized from 0.5 MW to 100 MW. The steam turbine generator sets are industry standard equipment that have highly reliable uptimes and feature rugged designs that operate in numerous industrial sectors including waste-to-energy applications. The base design includes a complete turbine generator package and GCES will work closely with clients to ensure that all design and operational requirements are met. The turbine generators can be direct-drive or geared and depending on the specific application, solutions include a variety of configurations – condensing or non-condensing, single or multi-valve, single- or double-automatic extraction, or mixed-pressure designs. The generated electricity from the turbine generator is now ready for connection to the client switchgear or transmission lines via a power generation metering station at the battery limits of the Waste-to-Power facility.
- Power Transmission
The transmission of power beyond the battery limits of the WTP site is typically the responsibility of the utility company. GCES works with utility companies on various levels to complete the overall power generation program. At the completion of the project and upon power generation start-up, GCES typically transitions into an operate and maintain function working in conjunction with the authority having jurisdiction (AHJ) over power transmission. This functionality is accomplished through a power purchase agreement (PPA) with the utility.
- Easily transported
- High ROI
- Compared to other emission control technologies, RTOs are particularly reliable
- Carry a low operating cost
- This high energy efficiency rates around 95%, and can be as high as 99%
- Greatly reducing fuel consumption
- Design simplicity
- No metal expansion issues
- High thermal efficiency
- Achieve high levels of VOC destruction to keep processes well below required DRE emission levels
- Adjustable stack heights
- Reactor has ceramic lining which reduces cracks and spallings allowing for a longer product life
- Easy installation
- Ceramic media beds absorb heart and recycle up to 95% for powering the equipment reducing fuel costs
- A digital controller allowing proper maintained temperature control
- Weatherproof, high-density steel enclosure, allowing the processing of highly concentrated exhaust streams
- Modulating burner
- Typical sizing from 300 to 60,000 SCFM
- Custom built, turnkey systems
- Adjustable stacks and multi-bed configurations
- Option of force, or induced draft fan arrangements
- Designs available for smaller or restricted spaces
- A variety of material options to withstand corrosive and high temperature exhaust streams
- Primary and secondary heat recovery systems
- Control panels, that are built in-house
This breakthrough CH4 Regenerative Thermal Oxidizer (RTO) was designed specifically for VAM projects. The VAM RTO allows Gulf Coast Environmental Systems to offer a financially superior solution to VAM projects without compromising on safety or efficiency. If you would like to learn more about our VAM technology, please email us at email@example.com, or call us at 1.832.476.9024.
To see even more about GCES’ involvement in VAM Projects, see GCES VAM Presentation-PDF