IDGTE Technical Paper Efficiency Gains by Bottoming Reciprocating Engines with an ORC By: Thomas Clark, MS Engineering Chief Engineer ElectraTherm, Inc. Introduction Reciprocating engine power generation efficiencies are well defined and understood, but significant increases are hard to find, costly and could add additional complexity and maintenance to the end user. One consideration is to investigate the value of the waste heat created by the engine, where in most instances today waste heat is just released to the atmosphere via the engine’s radiator and exhaust. Organic Rankine Cycle (ORC) technology is not new, but in recent years with the development of smaller packaged commercial ORC units, new and existing reciprocating engines are being retrofitted to turn the wasted thermal energy into increased power output. With the commercialization of lower temperature ORC systems, jacket water and exhaust are excellent sources of energy that can be converted into fuel savings. The ORC uses this previously wasted heat for additional fuel free, emission free power. ORC configurations can utilize either high temperature (exhaust), low temperature (jacket water) or a combination of both, demonstrating fuel efficiency gains up to 12%. The cooling power of the ORC also allows it to act as the engine’s radiator – saving on capital and displacing up to 30% of the ORC’s initial upfront cost. Instead of purchasing a radiator, an integrated ORC can become a radiator with a payback. For systems consuming diesel fuel, paybacks in fewer than 2-3 years are achievable. This paper demonstrates the potential of low temperature ORC technology coupled to reciprocating engines with applications throughout many industries. Also described is information about technical aspects of ORC machines, including the specific differentiation of ElectraTherm’s technology, fleet experience, robustness of design, and other attributes to consider when choosing an ORC for engine applications. The paper identifies specific examples and experiences from ElectraTherm installations in Europe and North America. Finally, the paper identifies important site considerations and payback scenarios analysis for engine users to have a full understanding of a complete project. Organic Rankine Cycle and How It Works The ORC process follows that of the steam engine, with the principle difference being the replacement of water with a much lower boiling point working fluid. Consider the ORC a refrigerator running in reverse, i.e. heat flow across a difference in temperature generates power. See the basic cycle in Figure 1.

Figure 1 Basic ORC Cycle

Steps in the process include: 1. Surplus heat is used to boil a working fluid in an evaporator. 2. Under pressure, the vapor is forced through a twin screw expander (the power block),

turning it to spin an electric generator. 3. The vapor is cooled and condensed back into a liquid in the condenser. 4. The working fluid liquid refrigerant is pumped to higher pressure and returned to the

evaporator to repeat the process.

Replacing water and steam with alternative low-boiling point fluids allows a modified version of the traditional Rankine cycle to successfully use heat which is typically at temperatures far too low to drive a steam engine to produce electricity. Such fluids include organic molecules, e.g. hydrocarbons like pentane, or hydro-fluorocarbon refrigerants, hence the moniker Organic Rankine Cycle. ElectraTherm’s ORC waste-heat-to-power generators, called Power+ Generators™, use a hydro-fluorocarbon called R-245fa (1,1,1,3,3-pentafluoropropane), a nonflammable, nontoxic liquid with a boiling point slightly below room temperature — about 15°C (58°F). Specific Differentiation of ElectraTherm’s Technology ElectraTherm’s proven patented twin screw expander enables its heat-to-power generating system to make electricity from waste heat instead of fossil fuel. ElectraTherm’s Power+ Generator represents a dramatic change from radial or axial turbine technologies, providing a more cost efficient, robust machine to generate fuel-free and emission-free electricity from a variety of heat sources. The twin screw expander offers distinct advantages for low temperature small-scale ORCs. These advantages include a simple and compact design, low speed operation with the ability to handle heat input variations and dual phase flow of the working fluid, significant part load capability, no gear box or oil pump, attractive payback and proven technology. This technology uses synergy based on proven refrigerant equipment and has many years of experience and reliability. The twin screw expander has a rotational speed of 1,800 – 4,900 RPM, considerably less than turbo expanders. Unlike high speed turbo expanders, screw expanders are robust units that tolerate “wet” dual phase flow. This allows the Power+ Generator to utilize more cost effective and compact heat exchangers that tolerate perturbations in both temperature and flow with turn down ratios of 6:1 available on demand. This is particularly advantageous in low temperature waste heat streams such as reciprocating engine jacket water. Through a patented lubrication scheme, the Power+ Generator design is simplified and eliminates lubrication reservoirs, oil coolers, pumps and land filters, creating a simple, robust and efficient system with fewer parasitic loads and maintenance requirements. Figure 2 shows a significant portion of the waste heat on a reciprocating engine is at low temperatures and this can vary greatly depending on engine throttle position. Figure 2 Reciprocating Engine Energy Split

This level of heat rejection is common to diesel, natural gas or biomass-powered reciprocating engines. Exhaust stack gases from virtually all combustion processes (ovens, kilns, furnaces, incinerators, thermal oxidizers and boilers) contain a large fraction of the original energy of the fuel

consumed. When this heat is recovered and converted into electricity, the overall plant efficiency increases. In addition to heat incidental to industrial processes, heat accompanies alternative energy processes such as geothermal, biogas, solar, biomass and oilfield geothermally-heated co-produced fluids. Historically, low grade waste heat has been ignored for several reasons:

1. Low-temperature waste heat can’t drive conventional heat engines such as water-based Rankine cycle systems (steam-turbine power plants). A lower-temperature method of converting this heat into electricity is needed.

2. Though the total amount of heat can be very large, it is geographically diverse. There’s insufficient heat available at individual process sites to utilize the most commonly available heat engine solutions, typically rated in megawatts. The distributed nature and variation of available waste heat sources demands smaller, modular and distributed generation technology previously unavailable.

3. Industries produce heat as a byproduct of their primary enterprise, so they generally don’t consider waste heat to power as an integral part of their operations. Often, sites do not have the personnel with the skills or desire to recognize a power generation opportunity, design and install heat capture and ORC hardware, or operate and maintain power station-type equipment. A viable solution must be easy to install, operate and maintain.

4. Finally, low relative energy costs, as well as the historically intangible nature of the environmental benefits associated with reduced emissions, made the payback period of small waste-heat-to-power equipment too long. However, rising costs of energy — including the environmental costs of fossil fuel combustion — coupled with enabling new technology, have reduced the return on investment for waste heat-to-electricity conversion equipment.

ORC low-temperature heat energy can be utilized from exhaust heat, jacket water or both, and converted to a valuable form of energy such as electricity. ORC technology is bound by the same laws of thermodynamics that apply to the engine itself; heat must be rejected. Figure 3 shows heat flowing from a high-temperature [TH] through the working fluid of the ORC and into the cold sink [TC] thus forcing the working substance to do mechanical work, in this case, on a generator. Figure 3

The ideal fraction of energy or work that is theoretically recoverable in a heat engine is limited by the Carnot efficiency equation, given as: 1 - (TC / TH) When the temperatures are measured on an absolute scale, in Kelvin or Rankine degrees, about one third of the theoretical maximum is recoverable as electric power output from low temperature ORCs, resulting in an ORC conversion efficiency between 6-12%. Although the numbers may seem small, the fuel source (waste heat) is essentially free. The heat is already going to waste, or in some cases costing money and energy to remove from a process. The heat leaving the ORC condenser can

also be reused, though not for generating more electricity because of its low temperature. This low grade heat can be useful in low temperature heating applications such as district heating, greenhouses, aquaculture, domestic hot water preheating, radiant heating, swimming pools and maintaining the temperature in an anaerobic digester, etc.. ORC Generators – The Most Efficient Cooling Device There are multiple benefits to integrating an ORC heat to power generator with an engine genset to make it an efficient engine cooling device. See Figure 4 for the engine/ORC schematic showing the single cooling device configuration, where the engine’s radiator is eliminated. The first benefit is clear: there is additional electrical output from the conversion of the waste heat to electricity with no additional fuel consumption or emissions. Second and less obvious is the reduction or elimination of the parasitic load from the engine cooling fans. The Power+ Generator acts as the radiator, allowing the engine-driven radiator fans to be disconnected (or never purchased). Without the parasitic load of the radiator, more work can be performed by the engine to generate additional electricity. The Power+ Generator electricity output combined with the engine’s reduced parasitic load account for up to 12% fuel efficiency gain depending on engine size, configuration and ambient temperature of the site. Figure 4 Single cooling module for an engine/ORC combination

Depending on the engine size, the ORC cycle can be further optimized to make the best use of the available heat. If the exhaust is not available due to emissions control hardware, or if it is already captured for another use, then the ORC can be tailored to run just on the jacket water. Figure 5 illustrates this configuration.

Figure 5 engine/ORC combination running only on the jacket water

Another option, when exhaust heat is available, is to split out the heat streams coming into the ORC cycle. The lower temperature jacket water provides the preheat duty of the cycle, and the higher temperature exhaust heat provides the evaporation duty. Figure 6 shows this “Dual Heat Stream” approach. This configuration has the advantage of maximizing the temperature going into the evaporator which helps to drive a large temperature difference between the hot and cold sides of the cycle. The higher the temperature difference across the cycle, the greater the power output from the ORC. This is especially useful in areas of high ambient conditions, where the cold side of the cycle is elevated. Figure 6 engine/ORC combination running in a dual heat stream configuration

Background In the past, there were no proven commercial products for converting engine heat to power, so operators had little choice but to accept the heat loss to the atmosphere. Today, ElectraTherm has deployed more than 50 units worldwide with over 42 years of cumulative fleet experience at 96%+ availability. ElectraTherm is the leader in small-scale, low temperature, distributed power generation from waste heat. The Power+ Generator design and associated proprietary technologies allow power generation from low temperature heat ranging from 170-252°F (76-122°C). ElectraTherm’s waste heat to power technology converts various sources of heat into power, including internal combustion engines, small geothermal, biomass, concentrated solar and process heat. The primary market is waste heat from stationary internal combustion engines. Typical engine sites include:

prime power production in remote areas, island and developing nations, biogas gensets including landfill and waste water treatment plants, natural gas compression stations and renewable biofuels. The ElectraTherm ORC units are assembled as modular design packages with rugged structural frames that are forklift accessible. The designs are certified to ASME and CE standards and available in most voltage and frequency combinations, making units very compatible with most areas of the world. The ORC units are also available as engineered turnkey systems. The integrated assembly packages include Balance of Plant (BOP) equipment with both water and air cooling options contained inside a variety of available standard ISO shipping configurations. ElectraTherm currently manufactures a 35 kW unit that fits well with ~500 kW gensets (Power+ 4200 model), a 65 kW unit which fits well with ~800 kW engines (Power+ 4400 model), and our 110 kW unit (Power+ 6500 model), well suited for 1-2 MW engines. ElectraTherm’s experience to date with genset integration has been very successful. Applications include single engines and multiple engines utilizing jacket water heat alone as well as jacket water combined with exhaust heat. The ElectraTherm ORC also runs in dual heat configurations, and full radiator replacements where the Power+ is the only cooling source for the engine. Engines that have been integrated with the Power+ Generator include Jenbacher, Deutz and MWM engines in Europe as well as Cummins, CAT and Waukesha engines in North America. Experiences from ElectraTherm Installations Dutch Harbor, Alaska Installation In 2014, ElectraTherm installed three Power+ 4400 ORC generators utilizing the waste heat from three diesel gensets at the Dutch Harbor power plant in the remote Aleutian islands of Alaska. The generators capture the waste heat from the jacket water of two Wartsila W12V32 engines and one CAT C280-16 engine at temperatures as low as 165°F to generate approximately 75kWe net for the site. The power generated is sent directly to the grid, where residential costs of power are some of the highest in North America at $.45/kW. The City of Unalaska and the Alaska Energy Authority purchased the three ORC generators to utilize the untapped, existing resource at the power plant, anticipating approximately $250,000 annual fuel savings. In addition, the Power+ ORCs offset the radiators on the gensets significantly by reducing 8,000kW of thermal cooling work per month, an additional savings of about 500 gallons of fuel annually. The reduction of cooling loads is an additional benefit to the electricity generated when installations offset radiator cooling work. All three ORC generators utilize one cooling loop, sea water with an input temperature of 45°F. U. S. Department of Defense Engine/ORC Demonstration Continuous duty gensets provide base load power generation in diverse applications around the globe. However, high fuel costs and engine maintenance are pain points felt by operators as they deliver this critical service. A low maintenance path to significant fuel savings and lower emissions is what the U.S. Department of Defense (DOD) had in mind when they approached ElectraTherm to integrate the Power+ Generator with a Cummins KTA-50 1.1 megawatt engine. The DOD wanted to investigate the performance impact and economics for their diesel engine fleet. Between the DOD project and the 50 Power+ Generators in operation, ElectraTherm has demonstrated simple installation, mobility and low maintenance. The DOD demonstration proved the radiator with a payback model, where, the Power+ Generator replaced the Cummins engine’s radiator entirely and can deliver a payback of two years or less for diesel or heavy fuel oil-fired gensets. In effect, the engine’s waste heat becomes a source of cost savings by displacing the radiator’s capital cost and parasitic load, i.e. more power with a quick payback. Figures 7 and 8 show the design and final product for this project.

Figure 7 DOD funded ORC integration and replacement project

Figure 8 ORC/engine package ready to ship

Levice, Slovakia ElectraTherm commissioned 10 Power+ Generator 4400s in Levice, Slovakia in June 2014. ElectraTherm’s Czech distributor facilitated the deployment of the ORCs on a centralized district heating system in Slovakia as a means of increasing on-site efficiency and generating clean energy. To date, the site has accumulated over 20,000 hours of operation. The 10-machine installation, shown in Figure 9, utilizes the waste heat from two Rolls Royce gas turbines through a combined cycle. Exhaust from the turbines goes through a heat recovery steam generator. The lower temperature exhaust gas that cannot be fully utilized now produces hot water to meet demand for heating on the municipality’s district heating system. The remaining heat runs through ElectraTherm’s Power+ Generators to generate 400kWe of clean energy and attain attractive feed-in-tariff incentives. While combined cycle gas turbines are widely used throughout Europe for power generation and district heating, this is the first application of its kind to utilize ElectraTherm’s ORC technology to make additional power from the lower temperature waste heat. The Power+ Generators help the site reach maximum efficiency levels through heat that would otherwise go to waste.

Figure 9 ElectraTherm’s 10 Power+ Generator 4400s at a district heating plant in Slovakia.

Other Developing Areas of Waste Heat to Power As ElectraTherm continues to deploy units globally and in varying market applications, the company has discovered new opportunities to bring value to the marketplace. ElectraTherm has looked at the large number of stationary engines associated with natural gas compression, where engine heat is typically unused. It takes a significant amount of energy to transport the ever-growing supply of natural gas from where it is produced to where it is consumed. At natural gas compression stations, there are multiple opportunities to convert the existing waste heat streams to additional electricity and potentially more horsepower for increased compression and plant throughput. The existing waste heat streams can be converted to more power with no added fuel or emissions, using technology that is proven and established worldwide. The thousands of natural gas compression engines across the globe provide a great opportunity for waste heat to power. Most industrial processes, though designed with efficiency in mind, shed excess/unused heat in some form and in significant amounts. Other sources of waste heat originate from boilers, engines, furnaces, incinerators, etc., or it may originate from any other processes, including compression, chemical reactions and more. Conclusion - Identifying Important Site Issues and Payback Scenarios The key to any successful power project is to fully understand the requirements and to complete a detailed design analysis. The flow rates, temperatures, power costs and ambient conditions need to be verified to assure the system has an attractive payback. ElectraTherm’s application and engineering teams developed software tools that can predict performance for almost any heat source and ambient condition. This data can be run for a full year including daily temperature changes. Using this data, the team will predict the annual revenue and select the optimal ORC for each application. Obviously 24/7/365 operation, higher temperature heat sources, cooler ambient temperatures and electricity costs above $.15(US) per kWh will always make the payback faster, but not all the conditions have to be optimal to have a successful installation and every case should be analyzed. Many times the ORC adds additional benefits to the process beyond the value of the power produced, such as cooling, water savings or low grade heat that can be used elsewhere. Often feed-in-tariff incentives for renewables or federal/state or utility incentives can make projects very attractive. Figures 10 and 11 below are the performance tools that are utilized to analyze potential applications. ElectraTherm’s sales and applications engineers are available to complete this analysis and provide accurate payback scenarios.

Figure 10 Performance Analysis Tool

Considering the sample above with a net output of 80.5 kW from 1400 kWt the following payback estimate shown in Figure 11 can be completed.

Figure 11 Payback Analysis Tool

More Information ElectraTherm, Inc. is a renewable energy company headquartered in Reno, Nevada. For more information on ElectraTherm and its clean energy products, please visit www.electratherm.com. About the Author Tom Clark, Chief Engineer at ElectraTherm Tom Clark has 40 years of project development and project management experience in the areas of Organic Rankine Cycle power plant development, fuel cell power plant system design and custom component development of balance of plant equipment. He joined ElectraTherm from United Technologies Corporation, where his experience included managing the fuel cell mechanical and electrical engineering departments, as well as managing government DOE contracts. Tom has an extensive background in component design, development and testing and has been the Program Manager for all aspects of Balance of Plant (BOP) development for fuel cell and Organic Rankine system power plant systems. Tom received his Master of Science and Bachelor of Science in Mechanical Engineering at University of Massachusetts.