The power sector’s contribution to climate change is well known, with electricity the single largest emitter of carbon dioxide in Europe. The new European Emissions Trading scheme will certainly cause some changes to the sector. Only around one third of the fuel input makes useful electricity, so the electricity sector’s wastefulness causes over-consumption of fuel, large emissions of greenhouse gases and surprisingly large volumes of water usage.
As we all know, cogeneration offers a proven, cost-effective alternative by using the heat produced in electricity generation. Today, cogeneration saves Europe around 200 million tonnes of carbon dioxide per year and reduces the dependence on energy resources by 1200 PJ per year, equivalent to the energy consumption of Austria. Cogeneration has thus been identified as a key technical solution to improving Europe’s environment.
Cogeneration could, of course, do much more, with various studies indicating that at least 25% of electricity production could come from cogeneration in the next 20 years. The European Commission has recognized this and set a target for growth in a strategy paper in 1997. The target was to double the share of cogeneration from 9% to 18% in the electricity market by 2010. However, no progress was made towards the target in the following four years and thus the need was identified for stronger measures. Hence the Cogeneration Directive.
THE STARTING POINT
In 2001, COGEN Europe pressed the European Commission for a Directive on cogeneration to underline the importance of a legal framework to safeguard the future of the technology in the liberalizing European energy markets. The Commission brought forward a proposal in July 2002, but this did not live up to the expectations of COGEN Europe and others. The proposed Directive was a disappointing compromise, with modest demands, no targets and a restrictive 50 MW threshold policy recommendation.
Instead of setting targets, a method clearly not favoured among Member States, national authorities were to assess the potential for growth in cogeneration in their own countries, and then seek to fulfil that potential. The proposal recommended ways through which to focus support on the worthiest technologies, and offered solutions to legislating to improve access conditions to transmission and distribution networks.
A positive outlook for growth in the US
Biogas-fuelled microturbines already occupy a profitable niche for distributed generation in the US, particularly at small landfill sites and wastewater treatment plants. Here Christine Hurley looks at technology considerations, operating experience, and at market and site conditions, predicting continued growth for the technology.
Microturbines are demonstrating some unique attributes for running on biogas that enable them to compete against reciprocating engines – particularly at smaller sites. In fact, biogas applications are among the most promising early applications for microturbines.
Biogas is available from landfill sites, wastewater treatment plants, agricultural and livestock operations, food processing plants, gasified woody biomass, or other sources of organic waste. The combustible portion of the gas is methane (CH4). Most of the rest is CO2, with small amounts of nitrogen, oxygen, hydrogen, water (the biggest source of problems in biogas applications), hydrogen sulphide and trace elements. Microturbine manufacturers have taken note of the market opportunities available from biogas and have modified their systems to better handle the unique qualities of biogas and the impurities it contains – see Table 1.
LESSONS LEARNED FROM END-USERS
We have interviewed plant operators at nine wastewater treatment plants and two landfill sites operating a combined total of 60 microturbines, and found the following results in common:
- Site operators are generally happy with the microturbines and would recommend them to other landfill sites and wastewater treatment plants – particularly for smaller sites.
- Early landfill and digester installations had some start-up problems, including gas compressor failures, but those problems have been resolved for existing and new sites. End-users now report few problems with the operation of biogas-fuelled microturbines.
- New Capstone installations have a standardized gas-processing system that is simpler, more compact, and more reliable than previous installations.
- Compared with their previous electricity and heating bills, operators of landfill and digester sites are reporting quite significant cost savings as a result of using microturbines – particularly where state, local, and utility grants are available to help cover the capital costs of the equipment.
- Operators of several wastewater treatment plants and landfill sites said they specifically bought microturbines because the units run cleaner than engines.
On the last point, Capstone certifies that NOx emissions will be less than 9 parts per million (ppm), but its landfill and digester applications often only have 1-3 ppm. In contrast, emissions from uncontrolled reciprocating engines running on biogas can be in the range of 50-200 ppm.