Best Practice Guide

Food and Beverage Growers and Processors

Combined Heat and Power

Industrial CHP

Combined heat and power (CHP), also referred to as cogeneration, is the onsite generation of electricity and heating or cooling from a single fuel source.

To understand the advantages, it is helpful to first think about grid power. Electricity sent along the utility grid is about 27 percent efficient; as much as 73 percent of the input fuel is lost by the time power reaches end-users at the socket. About 65 percent of this fuel is lost as waste heat, a byproduct of generation. Another 8 percent or so is lost along transmission lines.

Main tunnel in cave barrel storage at Vineyard 29. Photo courtesy of Vineyard 29.View Details.

CHP limits these losses by recapturing waste heat and reusing it as a source of heating or cooling. Not only does this save energy otherwise lost up the smoke stack, it also reduces onsite energy demand. Several functions can be powered by waste heat rather than electricity or natural gas: steam generation, process heat, building heat, and process cooling, for example. The most efficient CHP systems have high thermal loads relative to electric loads, and can achieve upwards of 80 percent efficiency.

CHP also minimizes the distance electricity has to travel between generator and end-use, so very little is lost during transmission.

Installing a CHP system is an expensive capital investment, but yields substantial energy savings. Like boiler systems, there are several fuel options that work well with CHP, so some businesses can achieve even further cost savings using waste products such as methane or biomass instead of fossil fuels.

For many businesses in California, CHP has another important advantage: reliability. Since electricity is generated onsite, supply disruptions in grid power will not interfere with operations or building systems. In effect, CHP can act as backup generation. Given the high cost of disruptions to most manufacturers, the indirect benefit of increased reliability can be almost as significant as energy cost savings.

Any CHP system consists of three basic components: a prime mover, an electrical generator, and a heat recovery unit.

Diagram of a topping-cycle CHP system.View Details.

In a topping-cycle CHP system, a prime mover converts energy into motion. Common technologies include reciprocating engines, steam turbines, combustion turbines, and combined cycle combustion turbines. Microturbines, fuel cells, and Stirling engines are newer technologies that have begun to appear on the market, although they account for only a small percentage of all CHP systems in California - there were only 10 fuel cell systems, for example, out of nearly 670 CHP systems in 1999. As first-costs continue to drop, more businesses are likely to adopt these newer and more advanced technologies.

The prime mover connects to an electrical generator that produces part or all of a facility's electrical needs. Waste heat from this process is captured by some sort of heat recovery unit, such as an ICI boiler, a recuperator, an after cooler, or a heat exchanger.

Diagram of a bottom-cycle CHP system.View Details.

CHP systems can also work by capturing waste heat from an industrial process with high thermal loads, such as metal casting or smelting. This is known as bottom-cycle CHP. A heat recovery steam generator produces steam from the waste heat, which is used to power a prime mover and electrical generation.

Other CHP configurations are combined-cycle (both topping and bottom cycles are interconnected) or trigeneration in which electricity, heating, and cooling are all generated from a single fuel source.

Industrial Application of Cogeneration
The most common industries to use CHP are petroleum refining, petrochemical manufacturing, and pulp and paper manufacturing. Other, less energy-intensive industries also invest in CHP, such as food and beverage processors. Large commercial and institutional facilities, like hotels and high-rise office buildings, have found cogeneration to be cost-effective given the current trend of rising energy prices.

In 1998, the U.S. Department of Energy set a goal to double the use of cogeneration by 2010, which could potentially add 46 gigawatts of capacity - about the equivalent of 92 500-MW power plants. Analysis by the American Council for an Energy Efficient Economy (ACEEE) found that the DOE goal is not only achievable, but could be readily surpassed.

ACEEE notes that growth in cogeneration capacity can be attributed to four major factors:

  1. Technological advances that drive down costs while improving system efficiencies; new technologies have also made it possible to cost-effectively install smaller and more flexible prime movers.
  2. Existing boiler inventories are nearing the end of their useful life, and will soon need to be replaced.
  3. Environmental policies, particularly those directed at reducing greenhouse gas emissions, have increased pressure to adopt cleaner, more efficient energy technologies.
  4. Deregulation of markets that create new opportunities for small-scale distributed generation.

CHP is recognized as a important tool for reducing greenhouse gas (GHG) emissions. Indeed, European Union plans attribute 20 percent of total GHG reductions to the increased deployment of cogeneration. The United Kingdom relies even more heavily on CHP, assuming that as much as 50 percent of their GHG reductions will stem from its use.

Adding chiller capacity
Absorption chillers, although technically part of the HVAC system, are fueled by low-grade waste heat recovered from on-site electricity generation. Absorption chillers are available in capacities ranging from 100 to 1,500 tons and use environmentally benign refrigerants and absorbents instead of polluting chlorofluorocarbons. Although absorption chillers have a low coefficient of performance compared to electrical chillers, they are extremely cost-effective and efficient when used with a cogeneration system since very little electricity is used to power the chiller. Consider that the cost of cooling is about 22 percent of a building's total electrical expenses - the savings become clear.

Adsorption chiller. Image courtesy of Process Recovery Systems, Inc.View Details.

Adsorption chillers, like their close cousins absorption chillers, use waste heat instead of electricity to produce chilled water. Adsorption chillers eliminate the need for energy-intensive compressors and high voltage motors. Electrical needs are only about 0.2 kilowatts (kW) for a 30-ton model or 0.4 kW for a 150-ton model to power two small pumps and a digital control system. The coefficient of performance, a measurement of the chiller's energy efficiency, is 0.68 to 0.75 (a perfect 1.0 would indicate that no energy is lost converting waste heat to chilled water). By tying an adsorption chiller to a cogeneration system, a process known as trigeneration, the efficiency jumps even higher.

Relatively new to the United States, adsorption chillers were first produced in Japan by the Nishiyodo Kuchou Manufacturing Company in 1986. Since then, adsorption chillers have proven their cost-effectiveness in a number of applications in Europe and Japan.

Capacity curve: adsoprtion vs. absorption chiller. Chart courtesy of Process Recovery Systems, Inc.View Details.

Adsorption chillers can reuse waste heat from a number of different sources: cogeneration systems (becomes trigeneration), industrial processes, steam boilers, and even geothermal and solar heat. The temperature of inputted hot water (waste heat) can range from 194 F to 122º F, which in turn outputs chilled water as low as 37.4º F. Adsorption chillers can handle fluctuating water flow rates and water temperatures, normal conditions for waste heat recovery.

Adsorption chillers use water as a refrigerant, eliminating the use of Li-Br and other chemical refrigerants. A proprietary silica gel, good for 30 years, acts as an absorbent. Because chemical inputs have been eliminated, there is no corrosion of equipment, no need for chemical testing, and no hazardous leaks. As a result, not only are adsorption chillers safer, they require only minimal maintenance.

Because use of electricity and chemicals is minimized, adsorption chillers generally payback initial investment in about 1 to 3 years.

Cogeneration and the History of Energy

Cogeneration and the History of Energy
Combined heat and power (CHP), has been around since the beginning days of central power. Thomas Edison used CHP as early as 1882 in America's first power plant, selling both electricity and the waste heat produced as a byproduct. Although electricity generated by cogeneration was common at the turn of the century, these systems soon were replaced by central power as this became more readily available and easy to use.

Cogeneration in Food and Beverage Processing

Cogeneration in Food and Beverage Processing
Cogeneration capacity in food and beverage processing facilities accounts for about 16 percent of all California cogeneration, for a total of nearly 1450 MW - about the equivalent of three 500-MW power plants. About 70 percent of food and beverage cogeneration is from systems sized 1 MW of more, the largest of which is well over 200 MW. More than one-third of these systems rely on reciprocating engines as the prime mover, and nearly one-third using combustion turbines. Combined cycle turbines and boiler/steam turbines follow.
From http://www.eea-inc.com/chpdata/States/CA.html.

Business Examples

A dual 60-kilowatt microturbine cogeneration system was designed for and installed at Vineyard 29; two Capstone microturbines generate electricity from natural gas with about 28 percent efficiency. Waste heat from the microturbines is recovered with a heat exchanger to heat domestic and process water, and used to power an adsorption chiller that provides cooling capacity for the winery's heating, ventilating, air conditioning, and refrigerating (HVACR) system, including wine tanks and caves. A backup boiler and electric chiller provide added reliability, but are rarely needed.


When heating and cooling capacity is factored in along with electricity generation, the cogeneration system has a total system efficiency of over 80 percent (utility or "grid" power has an efficiency of about 30 percent, by comparison). Besides significantly better generation and transmission efficiencies, the cogeneration system considerably reduces greenhouse gas emissions per megawatt-hour of electricity compared with emissions associate with "grid" power.

Total energy cost savings are estimated between $24,000 and $39,000 per year. Conventional electricity and natural gas purchases would have been between $62,000 to $64,000 per year, whereas the cogeneration system costs about $25,000 to $38,000 per year (depending on the cost of natural gas). Payback on the McMinns' investment is expected in less than six years.


Resources

U.S. Department of Energy Distributed Energy Program supports cost-effective research and development aimed at lowering costs, reducing emissions, and improving reliability and performance to expand opportunities for the installation of distributed energy equipment today and in the future.

California Energy Commission Project Fact Sheet on waste heat driven adsorption chilling.

Northwest Food Processors Association Efficiency Practices and Emerging Technologies websites offer useful information and tips for the food processing industry.