|Los Angeles County Sanitation’s Calabasas gas-to-energy facility, which runs on landfill gas in California, US|
How better to extend the efficiency benefits of on-site CHP than by using renewable- or waste-derived fuels? Chris Lyons describes how his company is doing this with gas turbine technology.
The first modern use of cogeneration or combined heat and power (CHP) was in 1882 at the Pearl Street power station in Manhattan, New York. The plant, now operated by Consolidated Edison, is the United States’ largest commercial district energy and CHP system, providing space and water heating as well as steam, which assists food preparation at many restaurants, provides process heat to laundries and dry cleaners, and powers absorption chillers for air conditioning.
CHP is the technology with the most underused potential for increasing energy efficiency and reducing emission pollutants. Oak Ridge National Laboratory (ORNL), a US Department of Energy (DOE) science and technology laboratory, recognized this in a report which estimates that energy lost in the US as waste heat during electricity generation exceeds Japan’s total energy use. Greater use of CHP could turn that lost energy into steam for production processes and heat for water and building space, or even heat to drive absorption chillers for seasonal or process cooling.
Cogeneration can offer many benefits. A CHP system not only operates at higher energy efficiencies than conventional power stations, but can improve reliability and power security through its independence from external transmission and distribution networks. CHP is also a proven technology that can operate on renewable fuels and is considered one of the most effective means of reducing carbon dioxide emissions.
China’s Shandon Jinneng Coal Gasification Company
uses coke oven gas to fuel a 10 MW CHP plant
Efficient use of renewable-fuelled CHP also reduces the high water consumption of typical Rankine cycle steam systems. As the world population continues to increase, demand for water is becoming more and more of a challenge. Although many new power plants have restricted water consumption, units that use air-cooled condensers experience reduced efficiencies and power losses during hotter ambient conditions because of parasitic fan loads and higher condensing pressures. CHP reduces this water load by using the heat demands of industrial processes and other uses to condense the steam, thus saving the major loss of energy in power-only production facilities.
Despite these benefits, CHP’s contribution to meeting overall electric power demand only totals about 11% in Europe and 9% in the US. CHP’s growth has been hindered by volatile natural gas prices, lack of utility incentives to support implementation, and public policymakers’ poor understanding of CHP’s benefits. It will take many technologies and stakeholders to remove these barriers, safeguarding renewable energy and energy efficiency, and ensuring CHP’s prominent part in the solution.
CHP WITH RENEWABLES
Rising demand for sustainable power has increased the associated use of fossil fuels and renewables in power generation. CHP could provide the catalyst to expand this market. With the exception of hydro, most renewable power now comes from wind and solar. While solar works in conjunction with peak summer demands, wind power is more prevalent during off-peak demand. But both solar and wind power are unpredictable and put a high burden on grid reliability.
One of the biggest current issues with renewable power is integrating and balancing it with electric utilities’ overall demands. The ownership, construction and rate-basing of new transmission have also proved very difficult. The journey taken to get the 188 km Sunrise Powerlink transmission line project built illustrates these challenges. The Sunrise Powerlink project will bring 1 GW of solar power to southern California, a state that has been known for population growth and rolling blackouts. San Diego Gas & Electric finally received permission to build the $1.8 billion project after a four-year regulatory review process that involved more than 75 public hearings and millions of dollars in legal costs.
An industrial manufacturing facility running on landfill gas at Florida, US
While natural gas is CHP’s predominant fuel, biomass fires several systems. But biomass CHP is mainly found at pulp and paper mills, where waste bark provides a fuel source that meets the need for plants to be reasonably close to their source of fuel. While excellent systems operate around the world, including several in Scandinavia, the costs of transporting large volumes of woody biomass to thermal host sites limit opportunities for further growth.
Yet the amount of waste sources generated by densely populated metropolitan areas makes waste-fuelled CHP an attractive alternative.
WASTES AS FUELS
The average American throws away 2 kg of rubbish per day, according to the Energy Information Administration (EIA). The figure for Europe is slightly lower but still more than 1.4 kg per person per day.
Some waste is incinerated in Europe, partly due to the closing of landfills. But incineration has little appeal in the US due to concerns over dioxins and furans that plagued many waste incinerators built during the 1970s and 1980s. Since 1990, in fact, only a few municipal solid waste (MSW) or refuse-derived fuel (RDF) power plants have been built in America.
In addition to MSW, a host of potential waste organic sources can be derived from industries such as poultry and food processing. Gasifying municipal waste or any other biomass fuel source produces synthetic gas that can fuel combustion turbines or reciprocating engines. Reciprocating engines can utilize gases with as low as 120 BTU/scf (4.5 MJ/Nm3), although gas with such a low calorific value has an impact on engines’ efficiency and power ratings. Most reciprocating engines are also smaller scale and provide lower thermal outputs, which is not necessarily the best choice for CHP applications.
While gas turbines need about 250 BTU/scf (9.3 MJ/Nm3) to assure flame stability, burning gas with low calorific values actually increases power outputs slightly due to the excess volume of gas. Despite the need to compress this gas from atmospheric type gasifiers, combustion turbines can achieve net efficiency in excess of 70%.
The prospect of meeting national and global energy needs while minimizing the impact on the environment has presented real economic opportunities and driven the development of new technology at Solar Turbines, a company that has committed research and development resources to supporting renewable fuels for 30 years.
RENEWABLE PORTFOLIO STANDARDS
Many countries now have some type of required renewable portfolio standard (RPS). Individual states in the US mandate the RPS through their public commissioners. Progressive states such as California have mandated that 33% of their electric power comes from renewable sources by 2020.
While many electric utilities have pursued blending existing coal-fired power stations with biomass, they have found they are limited to about 10–15% without significant design modifications for the varying fuel characteristics. Plant retrofits are possible, but sites must go through complete air permit modifications and still operate at lower conversion efficiencies than CHP.
The growing need to meet these RPSs combines with the increasing desire to reduce greenhouse emissions as well as issues over ownership and rate-basing of new electric transmission lines to make renewable fuel-powered CHP plants an appealing solution. CHP’s high efficiency means that it not only reduces greenhouse gas emissions but also produces less than half the overall emissions of traditional systems used to generate power and heat independently. CHP also reduces transmission losses and the need to build new power lines, as it is implemented close to the point of consumption.
CHP has been successfully implemented in many projects. Here are a few in which Solar Turbines has been involved.
SC Johnson – landfill gas
At its headquarters in Racine, Wisconsin, US, SC Johnson installed a landfill gas-fuelled 4.6 MW Centaur gas turbine to provide 25 GWh per year of baseload power and steam. The Environmental Protection Agency (EPA) has ranked this more than 100-year-old, family-owned company eighth in its Top 20 On-Site Generation list and made the firm a member of its Green Power Leadership Club.
Bay View WWT facility – digester and landfill gas
In Toledo, Ohio, US, the local Bay View Wastewater Treatment (WWT) facility installed a combination digester and landfill gas-fuelled 12 MW plant using a Taurus 60 combustion turbine from Solar Turbines. The waste heat provides steam for both heating the digester tanks and producing incremental renewable power from a steam turbine generator. A similar, but larger, 35 MW plant serving Los Angeles County has operated on digester gas since 1984. This plant uses three Mars gas turbine generator sets from Solar Turbines and a steam turbine with extraction steam used to heat the digester tanks.
Shandon Jinneng Coal Gasification Company – coke oven gas
In China, the first US EPA International CHP Energy Star Award was presented to Shandong Jinneng Coal Gasification Company for using previously wasted coke oven gas to fuel its 5.5 MW CHP plant. The plant uses a Taurus 60 combustion turbine from Solar Turbines.
East Bay Municipal Utility District – digester gas
East Bay Municipal Utility District in Oakland, California, US, has recently installed and commissioned a Mercury 4.5 MW recuperated gas turbine that achieves nitrous oxide and carbon monoxide emissions well below California’s strict air pollution limits without the need for any add-on environmental controls.
Greenville car making plant – landfill gas
A car making plant in Greenville, South Carolina, US, pipes in gas from a nearby landfill to fuel its 10 MW CHP plant. At the heart of the plant are two Solar Taurus 60 gas turbine generator sets.
Paris, France – landfill gas
Outside Paris, France, Veolia Environmental Services has installed a 15 MW landfill gas-fuelled combined-cycle plant that uses a Mars 100 Solar gas turbine generator set, supplied by Solar’s European facility in Switzerland, Turbomach.
A district energy CHP facility in Ontario, Canada, with a
Titan 130 gas turbine generator set
Ataköy WWT plant – digester gas
In Istanbul, Turkey, the Ataköy WWT plant installed two 4.6 MW Centaur 50 Solar gas turbines, also from Turbomach. The combustion turbines burn digester gas and provide hot water and sludge drying, while eliminating pollutants that previously seeped into the Mediterranean Sea.
Johnson Controls – landfill gas
Johnson Controls, under an energy service contract to a federal prison in Somerset, Pennsylvania, US, makes use of landfill gas from the nearby Laurel Highlands landfill to fuel a Centaur 40 from Solar Turbines. This 3.5 MW gas turbine generator set provides power and steam for heating, laundry, and energy security.
These are just a few examples of how using renewable fuels in CHP applications makes sense for efficiency, sustainability and energy security. CHP’s growth has been hindered by volatile natural gas prices, a lack of utility incentives to support its implementation, and public policymakers’ poor understanding of its benefits. Meeting future sustainability goals will involve a host of technologies but efficient renewable-fuelled CHP systems that already exist can help address these issues.
Inconsistent government policies on viable qualified renewable sources of energy have made it difficult for some policymakers to understand the benefits of renewable-fuelled CHP and district energy systems. But as these benefits become recognized and government officials become better informed, this market will prove to be a winning solution for clean energy and a sustainable future.
Chris Lyons is the manager, Power Generation, with Solar Turbines Inc. Email: email@example.com