1. Introduction
In an increasingly energy constrained world, energy efficiency is not simply a matter of good practise but also an element of fundamental competitiveness and an economic necessity. In the basic tool kit of energy efficiency techniques cogeneration is a high efficiency approach to energy transformation: generating both heat and electricity with an overall efficiency of primary energy use of 80-90%. It is a concept which continues to attract innovation and find application in new sectors and capacities. In the near term it is a technology which has a great deal to offer in meeting the energy and climate challenges of the 21st century, modernising the concepts of electricity and heat supply with high efficiency and appropriate solutions for an increasing variety of customers.
Cogeneration (also known as CHP or Combined Heat and Power) is the simultaneous production of heat and electricity. The technology for cogenerating heat and electricity is mature and widely used with 11% of the European Union’s electricity being produced in cogeneration plants raising the overall efficiency of electricity production above that of the historical condensing power station approach.
Cogeneration is currently used in industry, agriculture, domestic and commercial energy supply and spans applications with capacities ranging from 1kW to hundreds of MW. It is a highly efficient energy solution that delivers substantial reductions in CO2 emissions. Cogeneration units can be found in different sizes and applications: from micro CHP (family houses), small-scale cogeneration (hospitals, schools, swimming pools and hotels) to large-scale industrial applications and district heating schemes.
Cogeneration drastically reduces this waste of energy traditionally associated with generating electricity in a condensing process by deliberately placing the generation process in locations where the heat from the electricity production can be used. Cogeneration is a heat led concept in the sense that the plant is located at the site of the heat demand to maximise the use of the heat, and electricity is generated according to the heat load available. The electricity is sometimes referred to as a by-product. By converting the energy close to the consumer of heat and power, energy losses both of heat and of electricity (low transmission losses for both heat and electricity) are minimised.
The diagram on the previous pagecompares the production of heat and electricity in cogeneration to separate production of heat (in the boiler) and electricity (in the condensing power station). In the upper half of the diagram the cogeneration unit has an efficiency of 89%. In the case of separate production far more fuel is needed because of the high losses in the power station and additional losses in the electricity network and in the boiler.
Cogeneration can be applied in all cases where electricity is produced by thermal combustion, and can be based on all combustible fuel types, whether fossil or renewable. By analysing the consumption patterns of individual heat users, cogeneration schemes can be optimised to supply specific needs, with maximum overall efficiency.
2. Technologies
Engines
Most small-scale cogeneration units are internal combustion engines operating on the same familiar principles as their petrol and diesel automotive counterparts. Engines run with liquid or gaseous fuels, such as heating oil, natural gas or biogas, and are available from 1 kWe to more than 1,000 kWe. Internal combustion engines have a higher electrical efficiency than turbines, but the thermal energy they produce is generally at lower temperatures and so they are highly suited to buildings applications. The usable heat to power ratio is normally in the range 1:1 to 2:1.
For very small-scale applications with a capacity between 0.2 kWe and 9 kWe, Stirling engines can be used. These engines are external combustion devices and therefore differ substantially from the conventional models. The Stirling engine has fewer moving parts than conventional engines, and no valves, tappets, fuel injectors or spark ignition systems. It is therefore quieter than normal engines. Stirling engines also require little maintenance and the emission of pollutants is low.
Gas turbines
Gas turbines have become the most widely used prime mover for large-scale cogeneration in recent years. The waste gases exhausted from the turbine have a temperature of 450°C to 550°C, making the gas turbine particularly suitable for steam supply. Gas turbines are not only used in large-scale applications; smaller units starting at around 400 kWe are available on the market.
Since the late 1990s microturbines have become available. They are derived from automotive turbo-chargers and are available from 30 kWe to around 250 kWe. Microturbines use less space than conventional engines and maintenance costs are lower. Moreover, the emission of pollutant gases is reduced, especially those gases that cause acid rain and ozone layer depletion. Electrical efficiencies are typically lower than in internal combustion engines.
Steam turbines
Steam turbines have been used as prime movers for large-scale cogeneration systems for many years. Typically, steam turbines are associated with larger power stations but also smaller units starting with 200 kWe are frequently used. The overall efficiency generally is very high, achieving up to 84%. Steam turbines run with solid, liquid or gaseous fuels, both fossil and renewable. The typical heat:power ratio of steam turbines is around 6:1.
Fuel cells
A new technology in the sector is the development of fuel cells for cogeneration. Fuel cells convert the chemical energy of hydrogen and oxygen directly into electricity without combustion and mechanical work such as in turbines or engines. The hydrogen is usually produced from natural gas by a process known as reforming. The total efficiencies of cogeneration systems reach 85 to 90%, while the heat to power ratio is in the range 5:4. Fuel cells with a capacity of 1 kWe provide heat and power to single family houses, whereas bigger applications of around 300 kWe can be used in commercial applications and hospitals.
Heating and cooling
Thermal cooling, incorporated in a trigeneration plant, is an area of current development and deployment of systems. The usage of waste heat from (micro) cogeneration systems or district heating systems leads to an increase of efficiency and profitability of these innovative systems especially in the summer periods.
There are two basic types of thermal chillers: absorption and adsorption chillers. For an absorption process a liquid sorption medium and for an adsorption process a solid sorption medium is used. The following technologies are available for thermal chillers at present:
- Water / lithium bromide – absorption chillers
- Ammonia / water – absorption chillers
- Water / silica gel – adsorption chillers
- Desiccant-Evaporative Cooling (DEC)
- – open adsorption process
These technologies differ in available cooling output, required thermal input and hot water inlet temperature and heat efficiencies of condensation (coefficients of performance, COP) which means the ratio of cooling output to thermal input.
3. The position of cogeneration in Russia today
In Russia about 30% of heat is produced by cogeneration plants. Heat-only-boilers account for about 45% of total heat produced and decentralised sources (industrial or own-producers) account for the remaining share of heat produced. Russian industry is highly energy intensive. In 2007, the industrial sector accounted for 50% of total electricity demand, a higher share than most other countries. Given its suitability for energy intensive applications, just over half of Russia’s 500 cogeneration plants are based within the industrial sector. Together, the iron and steel sector (30%) and the chemical and petrochemical sector (21%) accounted for over half the industrial heat consumption in Russia in 2007. Many major cities in Russia are centred on or close to a major industry and thus the heat from the industrial cogeneration supply can further be used for the lower temperature heat demand of district heating systems for the residential sector.
Russia has the world’s largest collection of district heating systems by far, with heat deliveries of about 1,700 TWh in 2007, almost 10 times more than the next largest system Ukraine (with a level just under 200 TWh) and Poland (just under 100 TWh in 2007). Just under three-quarters (74%) of space heat in buildings supplied in Russia is through district heating networks with the other quarter of the heat supplied by decentralised/individual heat sources. A large potential exists for energy savings in Russia’s district heating systems, especially through the reduction of losses from the distribution network and the implementation of energy efficiency measures. Given an estimated 20-30% of heat is lost through the heat distribution network before it reaches the end consumer, focus on reducing these network losses will be an essential first step. Only after this stage is completed will the installation of meters and heat-regulating devices in buildings to allow for demand-side management be effective.
Russia is in a strong position to take advantage of the high efficiency of modern cogeneration should it choose to do so. Many industries (particularly refining, paper production and chemicals) use cogeneration as key element of their competitiveness worldwide. Lighter industry (such as the food sector, process industries and greenhouse agriculture) are increasingly moving to adopt cogeneration as new sectors discover the benefits of the by-product of electricity from heat. A typical industrial application would be the Spanish ceramics factory pictured in figure 1 where a modern tiles and ceramics factory of 100,000 m2 uses a Centrax high efficiency cogeneration turbine plant to provide heat to its modern clay atomiser and to generate 3.7 MWe of electricity, or in Heineken’s plant at Zoeterwoude in the Netherlands where cogeneration is used in brewing process (see figure 2).
Growth worldwide in cogeneration is stimulated by new low carbon fuel types with considerable interest in waste to energy plants in certain countries and increasing interest in the use of cogeneration to maximise the primary energy efficiency of bio-energy plants. Denmark which, like Russia has an extensive district heating network is currently reporting an average primary energy saving (PES) of 25% compared to separate production of heat and electricity from the modern cogeneration technology installed in the recent period. Denmark has always made energy efficiency a principle element of their energy policy and made a deliberate choice to incorporate cogeneration into district heating networks to replace heat only distribution, thus introducing new electricity generation capacity, without expansive new build.
Mytishi Teploset, the district heating company of the Moscow suburb of Mytishi, engaged in an extensive program for the reconstruction and development of some of its district heating networks (2004-2008). The project comprised the reconstruction of 200 building substations and 120 km of double pipes to be replaced with pre-insulated pipes. The project was part of a major modernisation and new construction of the district heating systems in the region of Mytishi. The refurbishment of the heat network of the Mytishi led to the reduction of heat losses from 30% to only 12%. The project was funded using a World Bank loan of 600,000 USD from the World Bank.
4. European developments
The European Union is currently aiming to expand the contribution of cogeneration to the heat and electricity supply. There are lessons to be learned from this process. The EU produced the Cogeneration Directive 2004/08/EC to promote cogeneration in its territory. The Directive has been most successful in establishing a uniform definition for cogeneration requiring a certain level of energy efficiency before a plant is recognised as cogeneration. It has also set in place a review of the potential for cogeneration which is a necessary first step for many EU Member States, unfamiliar with the technology, to begin to assess how it might be applied. However, the reporting under the Directive has revealed many remaining barriers to the wider use of cogeneration. Firstly, the current volatility of energy prices plus the changing nature of pricing and subsidy of the energy and electricity market, makes it a difficult new business area to step into with confidence especially if you are a small player. Secondly but secondly but also crucially, crucially there are many barriers to connection for smaller cogeneration units trying to connect for the first time, largely arising from the novelty of the request and the competitive nature of the request.
The European lessons suggest that the correct supportive policy around grid connection and market access is necessary to promote cogeneration. Considering planned investment in industry and the large heat networks in place, the challenge in Russia will certainly include access to capital. However, to truly take advantage of cogeneration attention should also be given to encouraging new entrants at the medium-small scale and to creating a policy structure to support this. Observers in Europe are also beginning to comment on the need for energy strategy, particularly heat strategy, covering not just the near but also the long term in order to identify the correct infrastructure investments.
5. Conclusions
The International Energy Agency (IEA) began to report on cogeneration and district heating in 2007 as part of its responsibilities under the G8’s request to identify climate change mitigation actions. The IEA carried out a particular study on the Russian situation (IEA country profile: Russia, IEA DHC, www.ies-dhc.org) and makes several recommendations for the development of cogeneration and district heating.
Heat tariffs should be cost-reflective. As with electricity, heat tariffs should cover the full costs of heat production in order to maintain the longer term viability of the system. Ideally, before heat tariffs are increased, priority should be given to installing meters and heat regulating devices to allow consumers the ability to regulate their consumption.
Were the Mytishi renewal project to be extrapolated across the whole of Russia, this would equal a savings of almost 20% in input fuel to the heat sector or 30 bcm of natural gas. This type of saving could be used to offset the price of heat to appropriate customers in the transition period to cost-covering levels of heat tariffs.
Higher heat tariffs would help to cover maintenance costs necessary to allow for adequate refurbishment of heat supply networks across Russia’s district heating systems. As the maintenance of the systems improve, the overall efficiency of the system would improve with significant saving in heat losses.
Cogeneration both in terms of residential and industrial applications benefits from a medium and long term planning. The strategy should include medium to long term stable energy policy and widespread, stable financial and fiscal support for district heating system investments that reflect the full value of the long-term environmental and economic benefits. For example, grants, low interest loans, accelerated depreciation and tax exemptions can be used to assist potential investors in overcoming the additional up-front costs for investment. All these topics will be covered in a dedicated session on financing of cogeneration at the upcoming COGEN Europe and Euroheat & Power Joint Annual Conference “Teaming up for energy renewal – cogeneration and district heating” in Brussels on 2 June 2010 (www.conference2010.eu).
The existing infrastructure and the historic planning of industry with urban areas give Russia a unique opportunity to use modern cogeneration to maximise the efficiency of future electricity production. As the sector mobilises to accommodate new fuel types, new capacities and new applications the advantages both economically and socially of cogeneration for Russia would seem to be substantial.
