CHP and the city: Maximum efficiency, minimal space

Over half the world’s population now lives in cities, which account for two-thirds of the energy and 60% of the water consumed on the planet and also generate 70% of greenhouse gases. Natural gas-fired combined-cycle CHP plants can address these challenges by maximising fuel use and minimising space requirements in urban areas, write Lothar Balling and Michael Baum.

The world continues to be energy-hungry, with global demand expected to rise between 1.8% and 2% per year. This increase is driven primarily by booming regions in Asia, such as China and India. Soaring energy demand is also being fueled by the planet’s growing population and the need for greater mobility.

But where are these masses of people going to live, and how can a sustainable standard of living be secured? These are fundamental issues that policymakers must solve.

Dàƒ¼sseldorf’s new Lausward combined-cycle CHP plant will produce 300 MWth of district heat

It is commonly expected that the trend toward urbanisation will continue to accelerate. Additional megacities and large metropolitan areas will develop, resulting in the need to optimally use available urban space and establish infrastructure and services that support and enhance urban functional capabilities.

The challenges

Infrastructure requirements include the construction of housing, streets, hospitals and energy and water supply lines, just to mention a few. Functional services include the provision of electricity, water, heat (such as for district heating) and cooling for hospitals or warehouses. District heating applications range from traditional home heating to greenhouse heating supporting the agrarian industries.

Services are fed over supply lines that must meet growing demand. For most existing cities undergoing renewal programmes, the construction of new district heating pipe networks may be challenging. Planning restrictions and economics may sometimes outweigh ecological concerns. The optimal use of urban space dictates that electricity and heat generation facilities should not only fit into the available space, but should be customised to supply both electric power and district heat to save space for double installations.

Another consequence of creating megacities and large metropolitan areas is the production of great volumes of greenhouse gases in a relatively small area. Not only are greenhouse gases contributing to global warming, but they also pose considerable health problems to people living in densely populated areas. Industrial settlements, which are usually located in the vicinity of cities or large urban areas, may substantially contribute to that problem. Power generation facilities that supply industrial sites and dwellings should therefore be of low-emission design.

There is an inherent need for flexible power and heat generation because of fluctuating consumption needs. These needs may differ substantially by region. Whereas electricity consumption may decrease around midday on a summer day in Germany, consumption may steeply rise in countries where cooling aggregates run at high loads. For the latter, heat extraction driving absorption cooling machines may provide economical and ecological benefits.

Another major effect of the expected urbanisation is the increased consumption of water. Not surprisingly, policymakers have declared fresh water as the planet’s scarce resource in the future. It is expected that the demand for cooling water alone will increase by 50% by 2035 (compared to 2012 figures). Environmental organisations such as Greenpeace and BUND (Germany) are already expressing concerns that there will not be enough fresh water to cool power plants. Thus, such facilities should consume as little fresh water as possible to avoid conflicts between the daily water needs of the population and a stable power supply.

Cities will provide fertile ground for launching and achieving a green economy. This development can already be observed, notably in southern Germany, where many solar photovoltaic installations are seen on house roofs, turning consumers into small entrepreneurs. With renewable energy sources ” especially wind and solar ” developing into an important player in the current and future power generation mix, the effective integration of these fluctuating energy sources will require other plants to compensate for anticipated high loading and unloading gradients due to the fluctuating power feed-ins of large-scale renewable installations.

In summary, power plants constructed within the vicinities of megacities and metropolitan areas must fulfill a set of cross-functional requirements:

  • Flexibly produce power and heat as required;
  • Minimise environmental impact through a low-emission design in all aspects, including water consumption and pollution;
  • Be highly efficient and thus minimise fuel consumption and carbon emissions;
  • Be customised to optimally use the available site and minimise urban space requirements;
  • Be compatible with future market requirements with high renewable energy sources; and
  • Last but not least, run safely, reliably and predictably with flexibility in service outages.

Combined-cycle power plants (CCPPs) based on CHP technology can achieve these cross-functional requirements.

Combined-cycle CHP and urban space

Urban space development has come a long way, starting from early settlements around fertile grounds, to the origin of smaller cities, with some of them growing to megacities or being connected via high-speed transport routes into large metropolitan areas.

With over 50% of the world’s population now living in cities, it is no surprise that around 75% of the world’s energy consumption occurs in these dense urban areas. This, in turn, means that most of the pollution also originates in these areas.

But future cities will not only be affected by environmental degradation, but also by other challenges such as increased population, changing climate conditions and energy scarcity.

The requirements for urban space development must account for growth and density management, as well as energy performance, including establishing a modularised energy infrastructure to ensure a flexible and redundant operation of the energy system and hence a sustainable and vital city life.

Energy is needed throughout cities and metropolitan areas to support transport, heating, cooling and industries. In the coming decades, the demand for energy will be primarily satisfied by traditional fossil fuel sources such as oil, coal and gas. Since oil is considered a scarce resource, it is argued that energy scarcity may evolve as one of the future city’s problems if this dependency on oil cannot be substantially reduced by other means, such as the electrification of transport.

The energy performance of a city and its capability to reduce its per-capita energy consumption and carbon footprint is vital for a city’s survival and its ability to deal with future challenges such as rising energy prices and environmental shocks. Therefore it is no surprise that cities are already looking for ways to reach energy autarchy and rely mainly on renewable resources and environmentally friendlier and highly-efficient CCPPs with CHP technology.

Recent research suggests that an integrative approach of combining infrastructure modules will help establish so-called ‘resilient city centres’ which will enable effective and redundant infrastructure management.

By combining water and waste management, biomass fuel (e.g. methane) can be obtained and used as supplementary fuel to natural gas for a combined-cycle plant.

Today’s gas turbines can already burn a combination of biomethane and natural gas. The electric power of the CCPP is fed into the district grid and the heat is used for district heating, food production (greenhouses) and water purification services. The idea behind this arrangement is to use locally generated services (heat and power) for local use and thus avoid losses attributable to feeding in these services over long supply lines.

Siemens’ SGT5-8000H lies at the heart of Lausward’s new CHP Block F

An aging infrastructure

Another aspect is also worth considering for urban space development and the special requirements associated with energy infrastructure: the aging of the systems and the resulting challenges to developers.

The aging energy infrastructure problem becomes apparent when one considers that most of the current energy systems in the Western world were installed in the boom years following World War II and are nearing the end of their useful life. In the US, for example, half of the power plants are more than 30 years old and feed into electric distribution systems that are between 30 and 50 years old.

The need for replacement opens ways to provide new and more efficient technologies that can supply reliable and affordable energy. City developers will therefore look into ways to accommodate these new technologies and to improve the carbon footprint of the city’s infrastructure, such as installing CHP systems. With respect to district heating, planners will revise the possibilities to extend the city’s heating network to increase the degree of capacity utilisation of the CHP systems and avoid duplicate installations and unnecessary space consumption for installing separate heat and power systems.

Space restrictions may also apply to new installations. It is therefore preferable that new power plants be built on existing industrial (brownfield) sites. CCPPs can be flexibly designed to reduce the plant’s footprint and thus avoid sealing further greenfield areas. One example is the CCPP single-shaft design which arranges gas turbine, steam turbine and generator in a single line, allowing for a space-optimised arrangement.

With this arrangement, installations can be achieved on narrow sites. For wider but shorter sites, the multi-shaft design may prove to be more suitable.

The benefits

Urban space energy requirements range from population growth and energy scarcity over climate change to environmental degradation. CCPPs with CHP technology can provide substantial benefits for metropolitan planners and developers in improving energy performance and strengthening the infrastructure to counter present and future challenges.

Dàƒ¼sseldorf, the state capital of North-Rhine-Westphalia in Germany, has shown how these requirements and challenges can be solved with the installation of its new Lausward Block F CCPP.

With over 500,000 residents, Dàƒ¼sseldorf is a commercial and industrial centre. The city has committed to lowering its CO2 emissions by 10% every five years.

The local utility, Stadtwerke Dàƒ¼sseldorf (SWD), supplies around 15,000,000 MWh electrical power and around 1,300,000 MWh thermal (district heating) power to its consumers annually. SWD is extending its district heating network by 15 MWth/year to further lower the city’s carbon footprint.

SWD has three power and heat production centres: Flingern, Garath and Lausward, all located within the city limits.

In May 2012, SWD signed a contract with Siemens to install a highly efficient CCPP with CHP technology at its power and heat production center in Lausward. The new plant (Block F) will be a new benchmark with about 61% net efficiency in condensing mode and approximately 85% fuel utilisation factor. This new facility will replace an older CCPP plant, which is near the end of its useful life and will be placed on so-called cold-reserve status.

The heart of the new plant will be the SGT5-8000H gas turbine, which is one of the most efficient gas turbine available in the 50 Hz market. The size and efficiency of this machine allows for 300 MWth of district heating to be produced by this CCPP without supplementary firing. And by incorporating a special three-stage heat extraction design, the efficiency of the system can be maintained at high levels throughout the entire range of heat extraction. At the important load case of 150 MWth, the power loss figure is as low as 0.16.

In order to save valuable space, it was decided to build Block F in a brownfield area that was previously occupied by the large flue gas treatment towers of the former coal-fired power blocks. The available space is rectangular, allowing for a single-shaft design which limits the plant’s footprint. The design enables the maximum use of the available site and thus minimises urban space requirements.

Since Lausward and its power plants are clearly visible from the famous city centre, special attention was paid by SWD to achieving a high level of acceptance by the city’s planning department. Dàƒ¼sseldorf has its own urban lighting concept, which is especially apparent at night when major landmarks are illuminated. Lausward and its power plants is one of these special locations.

The Block F plant can be run flexibly to cover part-load and full-load cases for power and district heating export. Thanks to its powerful gas turbine and its high load gradient of 35 MW/minute and startup times of less than 40 minutes, temporal fluctuations of renewable energy feed-in can be compensated and can generate additional income by providing grid services.

The environmental impact of the new plant is very low because of its advanced burner design and high efficiency. The specific generation of kg of CO2 per kWh produced is extremely low in comparison with other fossil technologies. Specific carbon emissions are especially low where district heating is also included in the equation.

But most importantly, by integrating Block F into the overall modularised generation infrastructure, SWD can optimise its generation fleet on a short-term basis and achieve a high level of flexibility and redundancy for its power and district heating production.

Rather than choosing to import power from another centralised generation facility, SWD decided to follow its successful decentralisation concept and install the new plant within the city to keep transmission losses to a minimum.

The plant’s high efficiency will also help reduce the load on the Rhine River, which is used for cooling functions. Environmental studies conducted during the permit process showed that the impact of the new plant will be negligible and therefore the aspect of environmental integration can be considered as being fulfilled.

Planning for the future

Urban areas require special attention because of their sensivity towards climate change and pollution. Given the trend towards megacities and densely populated metropolitan areas, these problems will be critical in the 21st century. Policymakers and communities therefore need to revitalise their key infrastructures to avoid collapse and environmental shocks.

The latest combined-cycle power plants with CHP technology can help overcome these problems by maximising fuel utilisation and therefore reducing greenhouse gases substantially. The flexibility of CCPP operations enables the production of power and heat as required and thus satisfies demand when needed.

Dàƒ¼sseldorf’s new CCPP Lausward Block F provides an excellent example of how other urban space requirements are minimised by relying on highly-efficient technology.

This new plant will make Dàƒ¼sseldorf more resilient to present and future challenges and ensures its status as a vital, attractive and remarkable centre. Construction is already in full swing, core products are will be supplied in summer 2014 and the first grid connection is expected early 2015.

Lothar Balling is General Manager,GT Power Plant Solutions – Europe, Africa, Asia, Australia and Michael Baum is Sales Manager, GT Power Plant Solutions – North-West-Europe, Siemens Energy Sector.

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