Proceedings

Next generation biogas upgrading using highly selective gas separation membranes – showcasing the Poundbury project

Lems, R., Langerak, J., Dirkse E.H.M. , DMT Environmental Technology

(free)

Abstract

More and more effort is being put into the utilization of organic waste streams in anaerobic digesters, producing useful products such as fertilizers and biogas. DMT has been developing biogas treatment plants for over 25 years, closely following market developments. Due to governmental incentives and growing environmental awareness, it is becoming increasingly attractive to upgrade biogas to natural gas quality and inject it into the natural gas grid or use it as transport fuel. In this way, the biomethane can be utilized with the highest energy efficiency.

There are several biogas upgrading technologies, ranging from the most commonly used water scrubbing to highly sophisticated cryogenic techniques. Each process has its advantages and disadvantages, depending on the biogas origin, composition and plant location. However, with the latest developments in membrane separation, DMT has developed the Carborex® MS system. This system is based on an ingenious, multi-stage, high selective membrane system and offers the best economics for almost all situations, especially for plants up to 1,000 Nm3 /h. Besides the economics it offers several unique technical advantages.

The DMT Carborex® MS is a compact modular and containerized unit. Which applies high selective gas membranes for biogas upgrading. The upgraded gas has a methane concentration of >99% CH4 which greatly reduces the consumption and cost for adding propane. The biomethane can be injected in the local gas grid, or further compressed to 220 bar and used as vehicle fuel. This system has the highest energy recovery available (>98%) with only 0.18-0.22 kWh/Nm3 energy consumption and <0.5% methane loss, therefor maximizing revenues. The CO2 is recovered as >99,5% pure.

It is the only upgrading technology that also removes significant amounts of oxygen (up to 70%). In this article the theoretical back-ground of membrane systems is explained along with operation data of the Carborex-MS® plant at Poundbury (currently the largest commercial plant in the UK).

Keywords: Carborex® MS, Biogas, Bio-methane, CBG, Car fuel, Gas separation, Green gas, Highly selective gas membrane, Membrane separation, Upgrading

Introduction

The transition from fossil to renewable fuels is on its way! Biogas produced at landfills and/or digesters can be considered as renewable fuel since it is produced from organic waste. Most commonly the biogas is converted to electrical energy by gas engines with an efficiency of around 40%. increasing efficient to levels near 100% will require upgrading of the bio gas to natural gas quality. This can be done by various processes. upgraded bio gas (bio-methane) can be used as a vehicle fuel or injected into the gas grid (figure 2). Bio-methane used as vehicle fuel is one of the cleanest possible fuels, with hardly any CO2 emissions and very low local pollutants.

Upgrading of biogas mainly involves the removal of CO2, H2S and H2O from the raw gas. The CO2 is removed to increase the energy content of the gas. For Vehicle fuel this is important, because it increases the mileage of vehicles. When injecting biogas into the gas grid, a similar energy content will be required as that of the gas already present in the grid. The CO2 concentration is also important to ensure flame stability and energetic value for the end users. H2S needs to be removed to prolong the life time of the equipment,piping and burners since it is a very corrosive gas. If H2O is present in the gas stream, condensation can occur, which is highly undesirable and therefore, should be completely avoided. Table 1 shows the composition of raw biogas and the requirements of upgraded gas for several applications (grid NL/UK/DE and  vehicle fuel).

There are several biogas upgrading technologies, ranging from old-fashioned but highly reliable water scrubbing to highly sophisticated cryogenic techniques. Each process has its advantages and disadvantages, depending on the biogas origin, composition and plant location. However, with the latest developments in membrane separation, DMT has developed the Carborex® MS system, which is the perfect solution for almost all situations, especially for plants up to 1000 Nm3 /hr.

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