Most agree what matters to save the earth's environment is to minimize the CO2- contribution to the atmosphere. That should also apply to plants producing the fossil-free biomethane gas. Today, however, we have biogas plants in some countries that have process solutions where natural gas is used for the production of the biomethane. Is this a good way to produce green gas and which process is then the greenest?
To produce biomethane means that organic waste first must be broken down under anaerobic conditions so that biogas can be obtained with a methane content of 50-60 percent. The biogas is then purified and this process is usually referred to upgrading the biogas to biomethane to a methane content of 98-99 percent.
Malmberg is a leader in biogas upgrading and currently has over 100 plants producing biomethane using a water wash method. The process is well proven, simple and requires no heat. It is a robust process and it has been found appropriate for many different types of operating conditions.
The different process solutions normally used for upgrading biogas are Water wash, PSA (Pressure Swing Absorption), Membrane Technology or Amin process. The factors of great importance when deciding for a process solution are how much electricity is needed to run the plant's machinery and the heating demand the process requires. Another important factor is how much methane slipping the process and released into the atmosphere.
Process solutions have their pros and cons and just because of that you cannot compare factor by factor. The comparison should be about the process that produces the least CO2 equivalents. Thus, the process with least fossil impact to produce biomethane. It should be obvious that the entire environmental picture is taken into account in the decision of an upgrading process and be sure to calculate how much carbon dioxide the process actually uses to produce the fossil-free green gas.
In a direct comparison between the two processes that currently dominate the difference is significant. Amin process consumes large amounts of heat, which means that in some countries cheap fossil natural gas is used. On the other hand, methane emissions is only 0.1 percent. The water wash process has no need for heat but a methane slip of about 1 percent. Normally, this is handled in a parallel process with a RTO (Regenerative Thermal Oxidation) helping the methane slip to near zero.
For example there are plants in Europe today disregarding the actual environmental impact by using natural gas to produce the green gas. By comparing the two different processes CO2 contribution, made from given market data and the capacity of a plant typical of 1500 Nm³ / h, we see that the amine process actually contribute with 205 kg CO2/h. Water wash process including RTO only contributes 42 kg of carbon dioxide per hour. Which means nearly 5 times less CO2 contribution. Then we can start talking about green gas that is green in its true sense.