WASTE TO ENERGY
an application for RHI payment is made. However, the scheme rules that will apply are those at the date of registration; further detailed guidance will be published by Ofgem in due course. Guarantees are available for all capacities of biomethane, up to the injection of 250GWh per annum, but to be eligible for a guaranteed tariff rate, an applicant must follow three stages: • Stage 1: Provisional approval for a tariff guarantee • Stage 2: Application for a full tariff
guarantee • Stage 3: Application for full
registration
UPGRADING OPTIONS Te RHI reforms are expected to kickstart a second wave of activity in the UK biomethane market, which has already been the most successful sector of the anaerobic digestion (AD) and biogas industry over the past few years. Whereas biogas is only suitable for heat and electricity generation, once it is upgraded to a higher standard of purity, it can also be injected into the gas grid and used for the same purposes as natural gas. Te upgrading process removes CO2
and any
contaminants, thereby increasing the methane content. Tis upgraded biogas is called biomethane.
• Chemical wash, which uses absorber liquids such as glycol ethers or amines to remove the contaminants;
Tere are a number of different upgrading technologies on the market. Te main solutions are: •Water wash technology, which uses high pressure water to ‘scrub’ impurities such as CO2
, and H2 S from raw biogas;
• Pressure swing adsorption (PSA), which uses adsorbent beds to remove impurities;
• Cryogenic upgrading, which involves compressing, cooling and then expanding the biogas until the CO2
H2 from CH4 and N2 . , O2 is
condensed and can then be removed as a liquid;
• And membrane technology, which uses gas permeation to separate CO2
ADVANTAGES OF MEMBRANE All of these solutions are in use at biomethane facilities around the country, but in recent years, membrane technology has become the preferred upgrading solution for the majority of UK biomethane plants, largely due to its small footprint, low methane slip, minimal maintenance requirements and superior gas production. One of the most efficient membrane solutions on the market is the Carborex MS,
and
supplied by DMT Environmental Technology. Tis highly efficient membrane technology is available in modular units ranging from 40Nm3 biogas/hr to 15,000 Nm3
biogas/hr (and
higher), making DMT Environmental one of the few suppliers able to deliver the total range from small to large biogas upgrading installations worldwide. With an efficiency of more than 99.5%, the Carborex MS is a simple, easy to operate, plug & play system. It has a low energy consumption (0.22 kWh/ Nm3
biogas) and requires no additional heat – in fact, it offers heat recovery of >0.25 kWt/Nm3
biogas, which covers
the main energy consumption of an AD plant.
GUARANTEED SUPPORT AND PERFORMANCE Since constructing the world’s first commercial plant for upgrading biogas using a three-stage membrane system at Poundbury in Dorset, the company has continued to develop its technology to be even more cost effective and efficient, to help operators reduce downtime and increase revenues. Over the past six years it has installed over 30 systems worldwide, regularly achieving 98% operational availability for its client base. Te membrane technology has produced a quarter of a billion cubic metres of biomethane globally, which is enough green gas to heat 227,000 homes and power thousands of vehicles. Tanks in part to the RHI reforms, the company sees a robust future for the UK biomethane sector. Membrane technology is now a proven biogas upgrading solution. Already in use at the majority of UK biomethane plants, modern membrane systems such as the Carborex MS offer users a high quality, environmentally friendly and flexible upgrading experience, compared to other traditional high-rise, complicated or energy- intensive techniques. Compact, efficient and simple to use, membrane upgrading technology is perfectly placed to take the UK towards a green gas revolution.
There are several methods available to upgrade biogas to biomethane of a natural gas quality
42
www.engineerlive.com
Stephen MCcullough is UK business director at DMT Environmental Technology.
www.dmt-et.com
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