Extracting Biogas from Landfills

Landfills are a permanent fixture in our society today.  They typically have been open pit repositories for local waste, and in some cases, retired, and covered.  However, the biological reactions in these landfills create a marketable biogas that can be useful to the owner. 

The consideration of taking a raw biogas from a landfill and converting it to electrical energy or Renewable Natural Gas is fraught with many stumbling blocks.  First, and foremost, the raw biogas can contain well in excess of 5000 ppmv of Hydrogen Sulfide.  Since the biogas is saturated, this creates a significant corrosion issue for handling the biogas, and if not removed, yields sulfur dioxide in the exhaust of the energy conversion unit.  Next, the inclusion of siloxanes, which are almost always a part of the biogas are even more aggressive, as they evolve into damaging sand type powders in the engines. 

Lee Enterprises experts in biogas recovery offer solutions for treating these products that make their use a viable outcome, as opposed to just flaring the biogas.

ABOUT LEE ENTERPRISES CONSULTING, INC:  Lee Enterprises Consulting was founded in 1995, and has since grown to become the world’s premier bioeconomy consulting group with over 150 bioenergy and biochemical experts worldwide. The group’s experts are world renowned leaders in their field, selected based on their education, experience, and reputation and have done thousands of projects worldwide.  Lee Enterprises

Consulting is divided into sections including biofuels, biomaterials, biochemicals, feedstocks, technologies, land & natural resources management, food & livestock production, and cannabis/hemp and provide hundreds of services including business & financial, technical & engineering, project management, legal & regulatory, and a variety of highly specialized services like due diligence, market research, risk analysis, litigation support and techno-economic analysis. 

Contact: Wayne Lee, CEO
Lee Enterprises Consulting, Inc.
9821 Brockington Rd., Sherwood, AR 72120
Phone: 501.833.8511
www.lee-enterprises.com

Sequester Biogas from Landfills

Given the ideal circumstances, landfills offer a very large volume of biogas that can be converted to Renewable Natural Gas.  Landfills are typically very large, and when they have been designed to efficiently retrieve the generated biogas from the landfill, it is usually a very large volume, in excess of 1000-2000 SCFM.  This amount of biogas can be very attractive for re-injection into a pipeline, but the biogas itself demands a proactive approach to prepare it for such an end use.

Raw biogas from landfills rarely have more than 50% methane in the mix, and also include moisture at the saturation point, as well as siloxanes and Hydrogen Sulfide.  Add to this the complication of introducing Nitrogen and oxygen to the biogas, due to the vacuum methods of retrieving the biogas from the landfill, and you have a biogas mixture that is problematic at the very least.

Expert consultants who have many years of experience in this are reside at Lee Enterprises, Inc, and can guide the investor through the qualification process, to ascertain the ROI for the site.  Many times, just taking the biogas to a state that is acceptable to an engine is enough, so the gas doesn’t need to be flared. 

The next level of sophistication would be to remove the carbon dioxide, and any residual inert gases, such as nitrogen.  These steps require analysis of the product gas to measure the cost benefit of taking it to the next level.  Each site is unique, and each site in itself will change over its lifetime.

Contact: Lowell E Howard, PE
CEO - WC Energy Systems
Phone: 425-260-3354

Waste Digester Process

Digesters by definition are either in-ground, or above ground lagoons that are primary process vessels for waste generated by humans, animals, or fowl.  The general expectation by owners, is that biogas will be the constant effluent from these digesters.  The layman may assume that magically, bacteria converts the organic material to biogas, without much sophisticated technology required.  Nothing could be further from the truth.

Most animal waste digesters need to operate at the mesophilic bacteria ideal range, which is above 100 F to 110F.  This not only requires commitment to OPEX in the form of energy addition, but also implies that lower temperatures will yield lower biogas outputs as well. This is true, asymptotically in reverse.

In addition to primary limitations to biogas production, there are the other secondary players, such as ammonia that is a death warrant to the biogas producing bacteria, thus chicken waste is very difficult to convert with ordinary digester technology.  Ammonia needs to be removed prior to introduction to the digester.

Produced biogas almost always contains levels of hydrogen sulfide, and without preliminary treatment in the digester, will have to be removed post production, because pipeline specifications limit the levels of hydrogen sulfide.  These maximum levels are typically under .25 grains/100 SCFM.  If the gas is not going to a pipeline, then other limits on the gas quality will be defined by the end user.

One method of control of hydrogen sulfide is to inject air into the digester.  Also pure oxygen is a viable solution.  If we are going to RNG with the biogas, the air injection is very problematic, due to the nitrogen introduced to the biogas. Only the oxygen in air is used for the reduction of the hydrogen sulfide. The nitrogen must be removed prior to the injection site. Next, digesters are prone to upset.  This condition requires re-inoculation, or even more dramatic remedies. 

So, now that we have entertained all the negatives, where do we go from here?  It is not an exaggeration that RNG from any organic waste requires careful design, and real time controls.  Without these, the question is when the failure occurs, not if.

Expert chemistry and process consultants are the necessary partners required for the most successful outcome of an installation that converts organic waste to RNG.