Cleaning & Drying
Varec Biogas offers systems that efficiently remove moisture, hydrogen sulphide (H2S), and siloxane from digester gas. Allowing biogas to be free of moisture and particulate matter which is beneficial to run cogen systems and reduce energy costs.
Capitalising on the main production sources of biogas, whether through anaerobic digesters, lagoons, or municipal landfills, is essential. Varec Biogas Digester Gas Cleaning and Drying Equipment can be used in all systems to avoid severe damages to heat exchangers, turbines, gas engines and boilers.
For biogas to be used as an energy source, it should go through the following treatments:
1. H2S Removal
Biogas is produced during the anaerobic digestion of organic solids that contain small amounts of H2S. Depending on the influent wastewater composition, the biogas may contain concentrations ranging from 500 to 3000 ppm which needs to be reduced as:
- 3 to 5 ppm is when the odour becomes offensive
- 100 ppm is the required limit to prevent corrosion for many engine manufacturers
- 300 ppm is when the atmospheric concentration can become lethal
2. Moisture Removal
Moisture is also one of the most damaging components of biogas. While being the lead cause of corrosion, it can also build up in piping systems causing excessive pressure drops and unnecessary venting of digester gas.
3. Siloxane removal – if required
Some biogas sources have high siloxane contamination, resulting from waste from industries and households. During combustion, siloxane molecules will break down into silicon and oxygen, which can later form problematic compounds that can damage equipment, more specifically engines.
Mostly installed upstream of a gas engine generator or boiler, the 235 Series Gas Purifier provides a cost-effective system to remove most H2S.
How It Works
A bed of iron sponge consisting of wood shavings impregnated with iron oxide powder (Fe2O3) are loaded into two tanks forming a vessel. Each tank allows digester gas to be scrubbed either in series or in parallel. The wood shavings, supported on wooden pine trays, serve only as a carrier for Fe2O3 which is the active media for H2S removal. As the biogas goes through the tanks, it reacts with the media and the H2S is removed by reacting with the Fe2O3, forming ferric sulphide (Fe2S3).
When the iron sponge has fully reacted, exposing it to the atmosphere while ensuring that it is kept moist will regenerate it. While the iron sponge can be regenerated up to twice before it requires replacement, a continuous regeneration is recommended for long-term operation and increased efficiency. It requires a water spray wash system and a controlled amount of air injected into the gas.
Design Features
- Gas tight cover sea
- Heavy steel construction
- Drain connections
The 236 Series is the most cost-effective method for the removal of most H2S and should be installed upstream of a gas engine generator or boiler. Specifically designed for low-pressure biogas applications, it provides the most optimum space velocity for efficient digester gas/iron sponge reaction time. Its NFPA 820 approved and flame-retardant fibreglass construction extends more than four times its operating life.
How It Works
Like the 235 Series, H2S is removed by passing the biogas through the purifier where it reacts with a bed of Fe2O3 to form Fe2S3, water and heat. The iron sponge can be manually regenerated up to two times before requiring replacement. A continuous regeneration system allows for a lower maintenance cost and increased sponge efficiency by combining an air injection system with a water spray wash system.
Design Features
- Insulation option required for outdoor installation in freezing environments
- Media Removal System available
Downloadable Resources
Designed to remove moisture to protect downstream equipment, the 237 Series come with a safety scheme and automatic controls.
How It Works
The digester gas flows through a filter where particulates are removed. It then reaches the heat exchanger where it is cooled to a set temperature. Once cooled, water and other entrained liquid drop out of the biogas which is run through the compressor to reheat at a lower humidity level. If required, a third heat exchanger is added to cool off the gas once more to proceed with the siloxane removal.
Design Features
- Automatic Drainage using drip traps or condensate accumulators
- Skid Mounted Option to reduce installation costs and operational assurance
