CHP: Brewing up energy savings
Combined heat and power (CHP) systems—also known as cogeneration systems—generate electricity and usable thermal energy from onsite generator sets. CHP systems can reduce operating costs, increase electrical reliability, and reduce greenhouse gases. In the process of generating electrical energy, the mechanical work produces useful heat.
Instead of releasing the thermal energy into the air, the excess heat from the electrical generation process is captured and used beneficially, making the efficiency of a CHP system roughly twice that of a generator set. Typically, CHP systems are used at facilities with high heat load requirements, such as colleges, hospitals, industrial campuses, and yes, breweries.
CHP system types
CHP system types include back-pressure, steam turbines, gas turbines, and reciprocating engines. They are identified by the prime-mover technology, configured with a generator, heat recovery, and electrical connections.
Back-pressure or noncondensing steam turbines can be matched with multifuel boilers, industrial waste heat, and gas turbine waste heat. High-pressure steam is used for the rotation of the turbine blades. The low-pressure steam is used for processes and none of it is used for condensate. Gas turbines create high-temperature exhaust heat that is well-suited to high-pressure steam production required by process industries.
Reciprocating engines total more than half of the CHP systems in place in the U.S. They produce exhaust heat ideal for hot water production and generally have a higher electrical energy-to-thermal energy output than a standard combustion turbine.
Reciprocating engine generators are often chosen for their rapid startup times, high electrical efficiencies, ability to respond to changing load patterns, and proven reliability, especially with multiple units. Byproduct heat from an engine-generator set comes from several sources. These include engine jacket cooling water and heat recovered from exhaust gases.
Energy efficiency benefits of CHP
For many industrial users, natural gas-powered engine generation represents an ideal source for site electrical power, plus it offers significant byproduct heat from the engine for a wide variety of thermal applications. Today’s advanced engine generators have efficiencies well beyond gensets of a few decades ago. When paired with proper CHP design, these systems provide efficiencies of more than 85%.
"When recovering the surplus heat from the generator the overall efficiency of the plant can exceed 90%," said Alex Marshall, group marketing and compliance director at Clarke Energy, (i.e., 45% electrical efficiency plus 45% thermal efficiency)."
Using CHP in breweries
"Industrial applications, such as breweries, food processing, or tissue paper are great fit for CHP because both the thermal and power outputs are used making the overall system more efficient," said Dalia El Tawy, director of thermal power solutions in Distributed Energy Systems Center of Competence at Siemens Energy. "Depending on the load requirements of the application, the CHP technology can be determined."
"CHP or cogeneration has significant potential in the brewery industry," says Marshall. "Electricity and heat recovered from a gas engine can be deployed at high efficiency for useful onsite use. This gives the ability to reduce operational costs and to reduce carbon emissions. Converting the heat into cooling via absorption chillers is called combined cooling heat and power (CCHP) or trigeneration and can be deployed to support the cooling requirements of the brewery."
Marshall lists benefits of CHP for the brewery industry:
- Energy cost savings—Overall electrical and thermal efficiencies can reach 95% using a wide fuel range
- Resilient and robust power—You don’t have to rely on the grid alone to ensure your facility has the power it needs 24/7
- More environmentally friendly—Less fuel burned per MW generated at lower CO2 emissions
- Dry low emission (DLE) technology can sustain lower emissions levels while eliminating system water requirements
- Standardized design—A smaller footprint is scalable to your unique spatial requirements
- Flexible power—Thermal energy can be stored for use; electricity can be fed into the public grid or used for artificial lighting, and an optional full island lighting control system is available
- Simplified maintenance—Fast replacement and onsite maintenance is critical for continued operation.
Marshall explains that the processing steps of wort boiling and bottle washing require more than half of the thermal energy needed in breweries. Electricity is used for refrigerating purposes in storage and fermentation. "Because the temperatures of CHP thermal discharges range from 113°F to about 356°F (exhaust gas), large potential arises from low-temperature heat consumers, such as bottle washing, which is done at a temperature around 194°F, and filtration. Two main criteria positively affect the efficiency of CHP facilities in breweries: A larger number of low-temperature processes and a constant heating and/or cooling demand," Marshall said.
High energy renewable biogas can be created from byproducts of beverage production and wastewater treatment. Instead of considering them waste, they can be converted into electricity and thermal energy to be used in your process, significantly cutting operating expenditures. CHP also reduces your electricity costs, according to Marshall.
Although not every brewery requires sufficient heat to operate a CHP facility for their production, CHP also can be financially beneficial for smaller companies such as craft breweries. Because many also offer hospitality, the combined thermal demand of brewery and guest rooms serves as heat sink of the CHP plant. Thereby, separate sources of thermal energy for production and domestic heating become obsolete.
New Belgium Brewing Company, Fort Collins, Colo. is an example of a major craft brewery that has selected a CHP solution. New Belgium is the 4th largest craft brewery and the 7th largest brewery in the U.S. It produces more than two dozen different beers and about 960,000 barrels of beer annually. The company prides itself on environmental innovation, energy efficiency, conservation, and recycling.
Reasons for CHP—The City of Fort Collins was charging the brewery a large "plant investment fee" (PIF) for the construction of infrastructure to process the brewery’s high-strength wastewater in the municipal water system. Instead of paying the city’s PIFs, the brewery invested the money in a 225,000 gal/day onsite process water treatment plant, including anaerobic digestion. New Belgium uses the methane produced by the digester to generate renewable electricity and heat in a combined heat and power (CHP) system.
CHP system equipment and configuration—The first phase of New Belgium’s CHP system was a 264-kW engine with heat recovery, initially located within the Brewhouse and at the brewery’s process water treatment plant. The engine was manufactured by Guascor (the Guascor reciprocating product line has been acquired by Dresser-Rand; Dresser-Rand has been acquired by Siemens. The product line has been renamed "Siemens Gas Engines"), and the system was designed by a Belgium-based Continental Energy Systems. The engine is fueled by the methane-rich biogas from the brewery’s process water treatment plant.
The second phase of New Belgium’s system is a 500-kW Guascor engine, which also is fueled by biogas and is located adjacent to the Brewhouse. Natural gas is used to start up and shut down the engine to mitigate corrosion risk from methane. The engine is programmed to react to coincident peak notifications, and it operates approximately 12 hours per day. Heat generated by the engine is transferred into a hot-process water storage tank, which provides water for the brewing process. At the same time that the 500-kW engine was installed, the brewery added a second methane storage balloon to the process water treatment plant, expanding the brewery’s methane storage capacity.
CHP operation—The CHP system runs 10 to 15 hours per day, depending on the amount of available biogas and the time of day. It is set to start when the methane storage balloon approaches 100% capacity and continues to operate until the methane volume is at 20%. Strategic programming also is in place to assure the CHP is running during the utility’s peak loads. The New Belgium Brewing Company staff performs the required maintenance on the unit.
Users need to evaluate project feasibility on a case-by-case basis. In the case of natural gas-fueled CHP, users trade the capital costs of equipment and increased fuel costs for lower electricity costs. Electricity savings must exceed the increased natural gas, capital, and operating costs to realize project profitability.
Many large industrial energy users are good candidates for natural gas-fired engine CHP. If your installation uses large blocks of electric power, and at the same time needs hot water or steam for process or comfort applications, now might be the time to have a qualified engineer do a study of this option. And if it has been some years since you have done such a study, it might be time to take another look.
This article originally appeared in the Gas Technology Spring 2018 issue.