Biogas generated from landfills, wastewater treatment plants or other anaerobic digestor sources is 100% saturated. Before the gas can be used in an engine or turbine application, or upgraded to RNG or CNG, it must be dehydrated to some extent. Removing the majority of the water from biogas also reduces the likelihood of downstream acid formation, which can cause wear on pipes, valves, instruments and other important parts.
A high level of water content in biogas noticeably reduces its net heating value, otherwise known as its net calorific value. This can have a significant negative impact on the energy efficiency of the engine, boiler, or turbine the product gas is intended to fuel. In RNG applications, the moisture level permitted in pipelines is low, (usually on the order of <7 lb/mmscf), so biogas must be dehydrated and cleaned before injection.
Our custom-engineered chilling and dehydration skids are capable of reducing water content in your biogas to sufficient levels for your end-use. This is how they work:
The biogas enters a heat exchanger called the economizer, which pre-cools the gas coming into the system using the gas exiting the system. The biogas is sent to a second heat exchanger, called the primary heat exchanger, where it’s cooled to the required dew point with a chilled glycol/water solution. In the heat exchangers, the biogas is typically chilled to 4°C/ 40°F.
The chilled biogas enters a knock-out tank, where the condensed water from the gas is collected and drained using a combination of level switches and drain valves. The cooled gas is sent to the economizer to be re-heated by the incoming gas, while pre-cooling the new gas entering the dehydration system. Whether you are cooling 15 scfm or 8000 scfm, we can also modularize your system for easier handling, installation and use.
Accompanying the dehydration skid, our team will supply a mechanical air- or water-cooled chiller. The GraniteFuel chiller is designed to provide the dehydration skid with the required cooling load via a glycol and water solution. The chiller is normally non-classified and has to be positioned at a set minimum distance from the dehydration skid and other biogas upgrading equipment. The chiller can also be built with added capacity to provide cooling for other associated conditioning equipment.
GraniteFuel can create individual solutions to meet your requirements and integrate the chiller as part of your biogas upgrading system. Contact the GraniteFuel team today or explore our other solutions to find out more about how we help with issues like H2S and siloxane removal, CO2/CH4 membrane separation and fuel blending. To help you meet strict sustainability standards, we also offer integrated emissions control solutions.
H2S removal from biogas
Hydrogen sulphide (H2S) is a poisonous and destructive contaminant often found in biogas. It appears at especially elevated levels in biogas generated from swine and dairy manure. Removing hydrogen sulfide is often the biggest issue in upgrading biogas to biomethane. The available abatement technology options include those with a higher initial capital cost but relatively low operating costs, and those with lower initial outlay costs but high operating costs. Either way, the combined cost generally represents a significant portion of the overall biogas upgrading equipment budget.
Removal thresholds vary according to the application or end use the biogas is intended for. 500ppmv H2S or less may be sufficient for boiler applications, while some combined heat and power engines will only tolerate levels below 100ppmv. Utility pipelines have even stricter requirements, and often dictate concentrations of 4ppmv or lower in biogas before it can be injected into the pipeline. As well as ensuring that you meet target reduction efficiencies for a given application, removing H2S helps prevent damage to downstream equipment like instruments, valves, vessels and pipes. We design, manufacture, and integrate our custom H2S removal systems to meet your unique raw and product gas requirements.
Oxygen and Hydrogen Sulphide
Hydrogen sulphide (H2S) removal is a key consideration when commissioning a biogas upgrading project, with significant implications for investment capital and operating costs. Introducing oxygen into your biogas conditioning process as a form of H2S control has potential cost benefits. Injecting oxygen into the headspace or hood of the anaerobic digester can reduce the amount of H2S downstream. Furthermore, introducing oxygen upstream of most H2S medias can boost the media’s potential H2S capacity. Either of these strategies, or both used in combination, can have significant financial benefits for H2S mitigation.
These methods result in higher trace oxygen levels than are supported by RNG applications, however these can be removed with the GraniteFuel oxygen removal system. The decision to introduce oxygen depends on an analysis of the cost of installing and operating the O2 system vs the benefit of lower H2S removal costs. However, in most cases where there are high H2S concentrations, supplemental oxygen provides a comparative advantage.
GraniteFuel’s H2S Removal Solution
At GraniteFuel, our oxygen injection and removal technologies are designed to maximize H2S removal media capacity and lower your operating costs. We size and design H2S removal media tanks in configurations suitable for your biogas source material and the intended application. This can include vessels operating in parallel or in a series, with or without heat-tracing and insulation, and specific design attributes that function with different media types. If desired, we can also supply parallel or lead-lag valves, piping skids for gas-flow control and drip-traps for condensate control.
At GraniteFuel, we custom engineer your system for your raw gas and product gas requirements. Our considerable experience building durable, efficient biogas solutions is exemplified in our H2S product designs. To make sure we provide the correct solution for your given application, we factor in upstream and downstream attributes and consequences when determining how to remove H2S from your biogas.
Contact the GraniteFuel team today or explore our other solutions to learn more about how we help with issues like chilling and dehydration, CO2/CH4 membrane separation and fuel blending. To help you meet strict sustainability standards, we also offer integrated emissions control solutions.