Institutional facilities throughout the US are employing combined heat and power (CHP) to attain goals in energy efficiency as well as cost savings, resiliency, and greenhouse gas reductions.
In California, Kaiser Permanente operates seven outdoor Tecogen CM-75 Ultera CHP Modules at its 340-bed Roseville Medical Center. The 525-kW cogeneration system was started up in November 2015.
Kaiser Permanente South Sacramento operates three outdoor Tecogen CM-75 Ultera CHP Modules at its 217-bed South Sacramento Medical Center. The 225-kW cogeneration system was started up in January 2017.
The cogen system is designed to efficiently deliver simultaneous electricity and free heat recovery to satisfy a portion of the hospital’s needs. The electricity produced is used onsite to reduce purchases from the local electric utility.
At the same time, the high-quality (225°F) heat that’s recovered from the engines’ jacket and exhaust systems gets completely used in the campus’ heating and domestic hot water CM-75 Ultera Cogeneration Modules (DHW) systems. It is designed to reduce operation of the hospital’s existing boilers and eliminate the corresponding gas usage.
Kaiser is not only realizing economic savings, but a reduction in greenhouse gas emissions associated with electrical and boiler usage by about 40%.
The cogen modules are equipped with Tecogen’s Ultera emissions controls, designed to reduce the units’ NOx and CO outputs to low levels.
Kaiser has successfully run Tecogen cogen modules at several other hospitals for many years. While that was one consideration in selecting the module, another was the desire for an engine-, microturbine-, and fuel cell-based CHP system as was offered by Tecogen.
During its first two years of operation in Roseville, the cogen system has operated nearly continuously, achieving an actual on-line factor of 93.3%. The system’s performance has demonstrated that it equates to annualized operation of about 8,200 run-hours per year.
In South Sacramento, during its first seven months of operation, the cogen system has operated nearly continuously, achieving an actual on-line factor of 98.1%. That system’s performance has demonstrated it equates to annualized operation of more than 8,500 run-hours per year.
In the aftermath of Hurricane Sandy in 2012 in which heavy flooding caused a power outage and forced evacuation of New York University’s Langone Medical Center, in New York, NY, building operators elected to develop a CHP plant to provide power to the campus and provide energy independence in case of future emergency.
Elliott Group was tapped to provide a single-valve/single-stage 2.5 MWe steam turbine generator (STG) as part of an integrated solution to provide sufficient electricity to meet the medical center’s power and steam requirements, reduce utility costs, and provide energy independence. The installation of the CHP plant augmented emergency generators and boilers in the building to offer two distinct sources of backup power for critical areas.
“In regions where electricity or power generation costs are high, such as the Northeast US, there is a favorable economic justification for CHP,” says Anthony Weidner, North American sales manager for Elliott Group’s power generation team. “Coupled with favorable payback periods, CHP is an attractive, sustainable solution for facilities, institutions, and campuses with steam systems,” he adds.
Elliott Group manufactures steam turbine generators (STGs) for institutional and industrial applications, often in a CHP capacity. The alternating seasonal steam demand for heating and air conditioning at institutions such as universities, medical centers, correctional institutions, and corporate campuses makes these facilities well suited for an STG.
“Many institutions use pressure reducing valves (PRVs) to lower the steam pressure from the boiler to the required level for their heating, cooling, or process needs. While PRVs effectively reduce steam pressure, they also waste valuable energy. In parallel with an existing PRV, an STG allows consumers to lower the steam pressure and capture the wasted energy to generate onsite electricity, saving money and increasing system efficiency,” says Weidner.
Another CHP project exemplifies how natural disasters can be a driving factor for facilities to establish resiliency through CHP. While most of New York City was without power in the wake of Hurricane Sandy, the lights were still on and the indoor temperature was comfortable in buildings at New York University (NYU) due to the university’s new cogeneration plant.
During the hurricane, NYU isolated itself from the main grid and operated in “island mode” to maintain power, heat, and hot water for 22 buildings on the main campus and 37 other connected facilities.
A central component in NYU’s co-gen plant: two Cleaver-Brooks Max-Fire Heat Recovery Steam Generators (HRSGs), installed in 2008 to recover heat from the exhaust ﬂow of combustion gas turbines.
The HRSGs harness energy wasted in the combustion process when vented directly to the atmosphere. The natural gas-ﬁred cogen plant, completed in January 2011, is part of NYU’s sustainability plan. The university’s cogen system operates at close to 90% efﬁciency and also provides the benefits of safety and reliability.
NYU’s cogen process begins with natural gas fueling twin high-tech gas turbines, the rotation of which is used to generate 11 MW of electricity.
As the turbines work, hot exhaust is directed to the Cleaver-Brooks HRSGs, which boil water into 600 psig steam directed to a steam turbine electrical generator to produce an additional 2.4 MW of electricity.
After the steam has passed through the steam turbine generator, it is used to make hot water for the campus in two high-temperature heat exchangers and to operate a turbine-driven chiller to produce cold water for air conditioning.
According to NYU, the cogen system saves between $5 and $8 million in energy-related costs annually compared to its former system.
Building owners and operators have a number of choices from which to source CHP systems and their components. Tecogen offers both induction-based and inverter-based cogeneration. Its system uses a natural gas-fueled internal combustion engine to generate electricity which is fed into the building and reduces the facility’s electrical consumption and utility bill. At the same time, free high-grade waste heat is recovered from the cogeneration system’s engine oil, jacket, and exhaust heat.
The captured heat is used to offset fuel that would otherwise have to be burned at a site’s water heaters and boilers. A gas bill for space heating, domestic hot water (DHW), and process hot water—among other applications—is also reduced.
Waste heat captured from the cogeneration system also can be fed into an absorption chiller to be converted into cooling.
Real-time cloud-based monitoring and data analytics powered by GE Equipment Insight ensure that the CHP units are continuously analyzed to provide optimal operation and maximized savings.
The units are fully scalable and microgrid-compatible and can be installed in multiples from 10-kW to multi-MW systems. The units utilize CERTS microgrid control software.
Elliott Group designs, manufactures, and configures STGs with power ranges from 50 kW to 50 MW. An Elliott STG is an efficient, cost-effective means of producing electric power from the excess thermal energy in a steam system, from a conventionally fueled source, or from an alternative fuel source such as biomass.
A complete STG package includes a steam turbine, speed-reducing gear, generator, integrated control system, lubrication system, and baseplate. Elliott Group also provides installation and commissioning support, maintenance and operator training, and long-term maintenance programs. Models include synchronous or induction type generators and standardized designs up to 3 MW for lower cost and faster delivery. Elliott STGs operate in power applications such as CHP, waste-to-energy, and waste heat recovery. STGs are configured to a facility’s specific requirements, with an ROI of less than three years, depending on applicable electricity rates.
Elliott offers three main types of steam turbines. Single-valve/single-stage steam turbines have one set of rotating blades on a single rotor and one internal governor valve which throttles steam flow at the turbine inlet. Single-valve/multi-stage steam turbines have multiple sets of rotating blades on a single rotor and one internal governor valve which throttles steam flow at the turbine inlet. Multi-valve/multi-stage units have multiple sets of rotating blades on a single rotor, and multiple governor valves which throttle the steam flow at the turbine inlet.
Configuring an STG for cost-effective power generation depends upon determining the right mix of elements, including a defined steam supply, a clear understanding of how the electricity will be used, and whether the steam is also needed for other processes. In contrast to the relatively unchanging process requirements of an industrial plant, the varying steam loads of some institutional applications necessitate a different system approach.
“Generally, it comes down to the existing steam conditions and how the facility plans to use the STG,” notes Weidner. “A lot of facilities that do have a steam system are using it for some other purpose, whether that’s heating or process needs of some sort. In considering a configuration, a facilities manager looks at a load profile of thermal and electrical loads and tries to determine where that unit fits best,” he adds.
“You want to operate a turbine as much as you possibly can year-round, but some facilities have a much higher thermal load in the winter than they do in the summer, so that must be considered. When the customer is ready to look at a certain application, they give us the steam conditions and the steam flow, and we size the turbine according to their needs,” says Weidner.
Generators are available in a wide array of powers, voltages, and enclosure types and rated for indoor or outdoor use and for different hazardous area conditions. In some power applications, the generator is directly driven by the turbine. Others require a speed-reducing gearbox between the turbine and the generator. The gear is designed to enable the turbine to operate at a higher, more efficient speed, while the generator operates at its required speed of 1500 rpm (50 Hertz) or 1800 rpm (60 Hertz). The lubrication system can be integrated into the speed-reducing gearbox or provided as a standalone system for added capacity in more demanding applications.
A state-of-the-art digital control system integrates all of the components of the STG. Through its programming and user interface, the control system provides protection and supervision of the STG and optimizes operation of the turbine and generator. Control options make remote interface with existing plant control systems possible, or remote control from a central control room.
In a fully-integrated control system, operators can manage the systems in several modes such as island, black start, tandem, parallel generation, or grid-interfaced. These systems can be configured with a wide range of PLC controllers to facilitate communication with existing plant systems.
The digital control system features a touchscreen interface (HMI) and a PLC-based controller. Other features include auto and manual synchronizing with sync check protection relay, independent overspeed trip protection, multi-function generator protection relay, excitation control (automatic voltage regulator), network communication and remote access capabilities, custom-tailored instrumentation, and display available in multiple languages.
From its engineered boiler sector, Cleaver-Brooks offers a line of heat recovery steam generators that follow a gas turbine or a large reciprocating engine, recovering the heat to enable end-users to make hot water or steam.
“Heat recovery steam generators offer the most efficiency because they are allowing the primary combustion source—which is either a gas turbine or a reciprocating engine—the ability to recover the heat from that combustion instead of sending it into the atmosphere,” notes Kimberly Garcia, heat recovery steam generator sales manager, engineered boiler systems for Cleaver-Brooks.
In configuring a system to achieve the greatest efficiencies, Garcia advises that facility operators do their homework when deciding on doing a CHP project.
“There are a lot of different technologies out there that you can use to do combined heat and power,” she points out. “You have to make sure that everything balances out—the electric production as well as heat production. Work with a reputable engineering firm and use the manufacturers out there to help decide on the best technology that makes the most sense for your facility.”
On retrofit CHP projects, size becomes a factor in configurations, but a new system is essentially a greenfield application lacking prior constraints, Garcia notes.
Resiliency and microgrids are hot topics in terms of having a stable power production situation or scheme in place that includes heat recovery so as to possibly provide steam or hot water in the event of a utility outage, notes Garcia.
“That is something to think about and have in place,” she adds.
Cleaver-Brooks offers HRSGs for such applications as hospital and healthcare and building heat designed to offer lower fuel costs, lower emissions, and steam solutions.
The Max-Fire Series operates at 10,000 to 500,000 pounds per hour with gas flows up to 1,000,000 pounds per hour, a design pressure of up to 2,300 psig, and steam temperatures to 1,050°F. It is available to less than 2 ppm NOx. The Max-Fire is a customized packed heat-recovery steam generator with gas turbines from 1 to 95 MW. Its boiler incorporates an integral furnace in a single shop-assembled package HRSG combining a furnace and evaporator and superheater, if applicable, with a natural circulation design. The system is capable of steam flows up to 300,000 pounds per hour.
The MF (O-style) and MFA (A-style) models combine the water wall combustion chamber formed from membrane wall construction with an evaporator section in a single shop-assembled boiler.
The VL (O-style) and VLA (A-style) models offer an evaporator section with no furnace that is enclosed with membrane wall construction.
The system features include a completely shop-assembled boiler with integral water-cooled furnace utilizing membrane-wall construction for firing temperatures above 2800°F; vertical (top) and horizontal gas outlets to help meet tight space requirements; and a combination of bare and finned tube sections designed to provide efficient heat recovery.
Additional features include multiple finned tube designs for optimized heat transfer; large steam drums designed to ensure ample steaming area; choice of either hard or aluminum casing; downcomers on both ends of the boiler; and accommodations for selective catalytic reduction (SCR) and CO catalyst.
The Max-Flow high-temperature water heater is designed for hot water or fluid heating up to 2,300 psig. It features forced circulation and is available to less than 2 ppm NOx.
The Cleaver-Brooks Max-Flow boiler incorporates a fluid-cooled membrane wall construction for the furnace and heating coil enclosure. Max-Flow Thermal Fluid Heater and High Temperature Hot Water generators are available for most applications ranging from 20–200 MMBTU per hour.
The systems incorporate a fluid-cooled membrane wall construction for the furnace and heating coil enclosure. They are designed to be fitted with a register burner or to recover heat from turbine exhaust and supplemented with a duct burner up to 2,800°F.
Other features include an optimized flow pattern which controls film temperature and local heat flux rates; a combination of bare tubes and various degrees of finned tubes in a staggered or inline arrangement for optimized heat transfer and pressure drop; a horizontal or vertical outlet to fit any space requirement; and a choice of steel or aluminum casing.
The system can be custom-engineered to accommodate space requirements and it can also accommodate selective catalytic reduction (SCR) and CO catalyst.
The Slant-VC HRSG is designed for a steam flow of 10,000 to 150,000 pounds per hour, steam pressures of up to 2,300 psig, and steam temperatures to 1,050°F, and is available to less than 2 ppm NOx.
Cleaver-Brooks Slant series natural circulation HRSGs feature the Slant model and VC (Vertical Drum Cross Flow) models. Both are tailored to applications with gas-side inlet temperature less than 1,700°F.
The Slant model provides an integral steam and water (mud) drum positioned diagonally to maximize the amount of heating surface for a given shipping profile designed to create a compact design for efficient heat recovery.
The VC model is a drum-over-drum design suited for higher steam pressure applications, integrated CO/SCR (selective catalytic reduction) systems, and horizontal exhaust flow arrangements.
Features include the following: a cold casing design with 300 and 400 series stainless steel or A-242/A-588 inner liners, depending on the gas-side temperature and service; multiple gas flow options designed to conform to space restrictions and minimize cost; unheated downcomers external to the boiler casing; and single-pass design for lower gas-side pressure drop.
Other features: multiple casing options including membrane-wall construction, ease of access to tubes for inspection and maintenance, a compact design, and accommodation of selective catalytic reduction (SCR) and CO catalyst.
Cleaver-Brooks waste heat boilers come in A-, O- and D-style designs and operate at 10,000 to 500,000 pounds per hour, temperatures to 900°F, steam pressures up to 2,300 psig, and gas flow rates up to 1,000,000 pounds per hour.
Cleaver-Brooks waste heat watertube boilers are offered in a single-pass design or multiple-pass design including furnace/radiant sections.
The natural circulation designs have membrane-wall construction. The single-pass designs have the steam and water drums positioned parallel or perpendicular to the gas flow and can incorporate an internal or external superheater, soot blowers, and economizers.
Multiple-pass designs include a radiant/furnace section to temper the heat of the flue gases before entering the screen or main evaporator bank and are available in A-type, D-type, or O-type configurations.
Multiple casing design options include internally lined and insulated, refractory construction, or membrane-wall construction. A vertical (top) or horizontal gas outlet conforms to the space restrictions.
Other features include a combination of bare and finned tubes depending on flue gas recovery and full-length steam and hot water drums with manways on each end for ease of access.
Capstone Turbine Corporation recently expanded into the critical power market with two new Capstone C65 CHP projects at North American hospitals, notes Jim Crouse, Capstone’s executive vice president of sales and marketing.
The projects align with the company’s goals to target hospitals and other healthcare facilities that require critical power on a continual basis. Capstone microturbines are designed to significantly reduce operating costs and “allow healthcare facilities to take control of their energy resiliency and carbon footprint, making critical power supply more of a target market vertical going forward,” adds Crouse.
The C65 microturbine is designed as Capstone’s most efficient power generation solution when installed in a CHP or CCHP configuration, says Crouse.
“With efficiency levels of up to 80% for CHP and 90% for CCHP, critical power facilities like hospitals and medical centers can benefit the most as they are constantly using electrical and thermal energy to care for their patients and staff,” he says. “Hospitals require a robust and reliable energy source as well as backup power should there ever be a loss of power, making them an ideal application for the C65.”