Using biogas as renewable natural gas affords strong benefits, both economic and environmental. Among them is the expansion of the overall energy supply enjoyed by nation-states, regions and local communities. In addition, infrastructure related to biogas provides investment and jobs wherever it is located. Beyond these, the improvement of air quality due to carbon-neutral emissions is substantial. Of course, these contributions exact a cost: biogas plants are highly priced expenditures. Nevertheless, compression technology has made biogas into a transportable, storable, effective energy commodity that is expected to more than pay for itself over time. Does compression really make the difference?

Biogas and Its Purposes

Some contend that biogas has a history of employment dating back thousands of years. Whether that is true or not, a safe observation is that biogas was understood as an energy originator as far back as the 18th century. In essence, this gas is the product of organic decay when oxygen is not present. This process encompasses a wide range of materials. An animal carcass, for instance, or wastewater sludge; vegetative waste dumped by a landscaper; swine manure or deer droppings; and the food scraps in a family’s compost pile are all but a sample of organic matter.

When such biodegradeable material lacks oxygen, specific bacterial microorganisms start to break down the matter, forming new chemical compounds over a series of phases. When all decomposition is done, methane, carbon dioxide and other compounds — in much smaller proportions — are discharged from the rotting biomass. Given the modern exigencies related to energy independence and climate change, biogas — long an unsung alternative origin for energy — is receiving new appreciation for its capacity to generate electricity, heat residential and commercial buildings, as well as feed transportation vehicles. Compression is essential to this last economic activity.

Compressing Renewable Natural Gas

Before discussing the workings of a biogas compressor, we must understand the need for content purity. To comply with vehicle fuel specifications, the proportion of methane to all else should be at least 97 percent. This means cleansing the biogas of water vapor, hydrogen sulfide and carbon dioxide. CO2 will not impede the biogas performance but it surely occupies fuel tank space that could otherwise be filled with the upgraded biomethane. There are numerous ways to effectuate the cleansing of biogas. Their criteria for selection include the organic materials for biogas production; the scale of the plant or project; and the purpose of the purified biogas. Once rid of contaminating and unnecessary compounds, the biomethane is sufficiently unadulterated for injection into a pipeline, deposit into a storage tank or direct input into a transport vehicle.

Whatever the immediate destination, compressing the gas is the next step. If the biomethane is to be stocked for later use, the compression force is usually about 3,500 pounds per square inch (psi). If it is to be transported by tanker truck, that pressure can rise to 4,000 psi. Pipeline conveyance most often allows for 1,000 psi or less. These various pressure applications actually squeeze the biogas molecules to hasten their movement from one location to another. A biogas compressor may be needed at the point of collection to aid in cleansing the gas of water vapor and other detrimental compounds. Alternately, compressor of biogas is called on as the gas travels through miles of pipelines of diverse dimensions. Finally, closer to the point of retail dispensing, a biogas compressor machine can treat the gas so it conforms to all safety and health standards.

Renewable natural gas is frequently compressed in stages. The number of stages depends on its volume at standard atmospheric pressure and the intended pressure needed for movement or storage. A multi-phase compressor of biogas is composed of several cylinders of declining dimensions — the smaller the cylinder, the higher the pressure. Many systems employ hydraulic fluid to push a piston upward inside the cylinder until it obtains the desired pressure. This can be dubbed a reciprocating compressor since the piston creates positive displacement, releasing the gas at a smaller volume. Screw compressors, on the other hand, use two integrated rotors to condense the gas. Here the gas is drawn into the compressor by suction and moves through the threads of the helical rotors, thereby getting compressed and released at a higher pressure.

What Kind of Investment Does a Compressor Require?

As noted above, compressors come in variable sizes and designs. Biogas compressor price can range from modest to cost-prohibitive. Key to any investment, of course, is the return. When will the compressor pay for itself? That question is answered by the volume of biogas processed and sold. Yet other factors also come into play, including how well the compressor prevents leakage and performs at an efficient level. Operational costs — or life cycle costs — factor into any compressor investment as much as the purchase price.

In Summary

Compression opens up more avenues for biogas since it allows the gas to more easily move from place to place and — in addition — occupy less space in storage. As retail and wholesale demand for this renewable energy soure grows, the infrastructure of conveyance and inventory holding mandates the employment of compressors. These processing components are engineered in diverse sizes and configurations.