Enhance Flare Gas Recovery with Liquid Ring Compressors

Gas flaring—the process of burning off associated gas from wells, hydrocarbon processing plants or refineries, either as a means of disposal or as a safety measure to relieve pressure—has extensive ecological and economic impacts. Managing the risks of flare gas is one of the leading challenges facing the oil and gas industry today. While the composition of flare gas varies by application and facility, more than 250 hazardous substances have been identified in flare gas. These include carcinogenic substances such as benzopyrene, benzene, carbon disulphide, carbonyl sulphide and toluene. Dangerous metals, such as mercury, arsenic and chromium, as well as poisonous gases like hydrogen sulfide and sulfur dioxide, are also present. Flare gas is one of the major factors contributing to climate change. Oil production facilities around the world burn off approximately 140 billion cubic meters of natural gas annually, causing more than 300 million tons of carbon dioxide (CO2) to be emitted to the atmosphere. (1) These chemicals can have devastating impacts on local populations because they contribute to serious health conditions, especially in newly industrializing countries with significant oil production levels.

Flare gas also contributes to billions in lost revenue for oil and gas companies. The World Bank estimates the 140 billion cubic meters being flared every year would be worth around $20 billion. If the amount of gas flared off in a year was recaptured for energy production, it could provide about 750 billion kilowatt hours (kWh) of electricity, or more than Africa’s current annual electricity consumption. (2) Oil and gas companies should consider how to optimize flare gas recovery process—not only for the environmental impact, but also to recoup economic losses.

Flare Gas Recovery Systems

While the flaring of gas plays a vital role in plant safety and excess gas disposal, oil and gas operations need to reassess how they recapture these materials. One way to prevent toxic substances from entering the atmosphere is to use a flare gas recovery system. These systems can recapture up to 98 percent of emissions for use in other plant processes, such as the heating gas system. Flare gas recovery systems reduce noise and thermal radiation, operating and maintenance costs, air pollution and gas emissions, the risk of harming human health, and fuel gas and steam consumption. The compressor, a vital component of a gas recovery system, must be reliable and able to withstand the aggressive conditions typically found in oil and gas production, including below freezing temperatures, hot and humid climates, sandstorms and intensive sun radiation.

Liquid Ring Compressors

While there are many compressors available for flare gas applications, liquid ring compressors are attracting a lot of attention because of their design and reliability that make them ideal for use in aggressive environments. One reason for the liquid ring compressors’ reliability is that it uses a liquid ring formed from the operating liquid, instead of a mechanical piston, as an energy carrier to compress gases and vapors. Liquid ring compressors can compress nearly all gases and vapors without any metallic parts contacting one another, which is advantageous because sliding parts are subject to vibration and wear, which impacts efficiency and leads to increased maintenance, downtime and possibly mechanical failure. These compressors also use a double-shaft seal design, which creates a safer environment for the compression of flammable mixtures as well as toxic and environmentally hazardous materials. Liquid ring compressors use an impeller located within a cylindrical casing, which is filled with operating liquid (typically water). As the impeller rotates, the resulting centrifugal force forms a moving cylindrical ring against the inside wall of the casing. This results in a volumetric expansion in the section of the outflowing liquid ring, which causes the medium to be drawn in via the inlet port in the guide plate. In the area of the inflowing liquid ring, the volume is reduced, causing the medium to be compressed. After compression, the medium is discharged via the outlet port in the guide plate.

Three-Stage Compression

New liquid ring compressor designs use two impellers, which compress the medium in three stages, rather than one- or two-stage compression as with previous designs. This three-stage compression can result in lower internal losses, optimized intermediate pressures, higher isothermal efficiency and lower volume flow loss at high-discharge pressures. The three-stage design also can require less power and water consumption. These compressors may be a viable alternative for those operations looking to optimize current flare gas recovery system and reduce costs. With a smaller footprint, these compressors can have lower installation labor and expenses. Modern liquid ring compressors employ an easy access pullout design. Since the bearings and axial face seals are arranged outside the pump, they can be replaced without having to dismantle the complete compressor. This design can make it simple to perform routine maintenance on seals and bearings and can reduce associated maintenance costs.

Reliability, Efficiency & Maintenance

Flare gas recovery systems can reduce the environmental and economic impacts of flaring gas into the atmosphere. As more oil and gas operations contend with larger volume flows, they need to leverage compressors that are reliable, efficient and easy to maintain. Using liquid ring compressors that employ modern hydraulic and mechanical designs that create thermodynamic advantages is a significant way to optimize flare gas recovery, recoup lost revenue and guarantee a safe compressing process. References 1. The World Bank. “Zero Routine Flaring by 2030.” 2. Ibid.