How do Waste Heat Recovery Systems Work?

Since fossil fuels have a high cost and pose significant environmental impacts, heat energy is an asset that cannot be wasted. However, many industrial sectors overlook utilizing waste heat. Waste heat recovery systems can reduce wasted energy in industrial processes by using it as an energy source for the plant’s operations. When identifying a viable waste heat source, one must also identify a consumer of the available waste heat. Numerous heat waste recovery technologies exist to provide additional energy sources and lower a plant’s overall energy consumption. Heat recovery systems have been the subject of major research across industries to lower harmful emissions, reduce fuel consumption, and improve production efficiency.

What are the Types of Waste Heat Recovery Systems?

While different heat recovery technologies are available, many feature a waste heat recovery unit consisting of energy recovery heat exchangers. All waste heat recovery systems use the same principle to capture, recover, and exchange heat with a potential energy source in a process. Each system converts the waste heat into an extra energy source to reuse heat that would otherwise be released into the environment or go unused.

Industrial applications have several benefits when utilizing one or multiple of the waste heat recovery system types listed below. Some advantages of industrial heat waste recovery systems include reduced carbon emissions, lower energy costs, increased energy stability, and effective use of sustainable power as companies grow.

  • Waste Heat Powered Thermal Fluid Heating Systems

    Waste heat-powered thermal fluid heating systems offer a closed loop, liquid phase heat transfer system to capture wasted energy and transfer it to various users. These systems capture waste heat using a hot gas or liquid heat exchanger to heat a circulated heat transfer fluid in a closed loop. Then, the heat transfer fluid is circulated to one or more heat consumers.

    Sigma Thermal offers waste heat recovery systems with a complete closed loop, liquid phase that utilizes water, glycol solutions, and thermal oils. We have experience with a range of transfer fluids, so trust us to go through various options and design a system that is best for your needs.

  • Combustion Air Pre-Heat System (CAPH)

    A combustion air pre-heat system utilizes heater exhaust gases to pre-heat the incoming combustion air, resulting in a more energy-efficient utilization. CAPH increases overall efficiency and lowers system and natural gas operating costs. A CAPH provides an estimated over 93% (LHV basis) efficiency.

    The typical components of a combustion air pre-heat system include:

    • Air-to-air heat exchanger
    • Modified burner for elevated combustion air temperatures
    • Combustion air ductwork for the combustion fan to the heat exchanger and heat exchanger to the heater
    • Exhaust gas ductwork for the heater to heat exchanger and, if applicable, heat exchanger to stack

What Is Waste Heat Recovery?

Waste heat recovery is a process that reuses industrial heat energy that would otherwise be released into the atmosphere or disposed of. Industrial plants utilizing waste heat recovery methods can greatly increase their energy efficiency, which also reduces energy costs and CO2 emissions.

  • High-temperature waste recovery is recovering waste heat over 750°F. Waste heat in this temperature range has a very high potential for recovery and use in a wide variety of other plant processes.
  • Medium-temperature waste recovery is waste heat between 350F-750°F. Waste heat in this temperature range has good potential for recovery and use in a wide variety of other plant processes.
  • Low-temperature waste recovery includes waste heat below 350°F. Waste heat in this temperature range has potential for recovery, but a limited number of uses for other plant processes due to the low temperature.

How Does Waste Heat Recovery Systems Work?

Waste heat recovery systems capture and transfer the waste heat from an industrial process back into the system as an additional energy source. The extra energy source can offset the demand from an existing fired or electric heater,t or generate electricity using an Organic Rankine Cycle generator (ORC). Although all temperatures of waste heat can potentially be transferred into another energy source, higher temperatures provide higher quality waste heat and make optimizing waste heat recovery processes easier. The type and source of waste heat determines which waste heat recovery system is suitable for the available process heat consumers. Therefore, it’s essential to balance the quality of the waste heat and how it aligns with the requirements of the process heat consumers.

Knowing the maximum amount of recoverable heat from the highest potential of an industrial process ensures maximum efficiency from a waste heat recovery system. Use the following equation to calculate the amount of waste heat available from an exhaust gas source.

Q = V x p x Cp x 𝚫T

Q (J) is the heat content, V is the substance flowrate (m3/s), ρ is the flue gas density (kg/m3), Cp is the substance’s specific heat (J/kg.K), and ΔT is the substance temperature difference (K) between the system’s highest temperature at the outlet (Tout) and the temperature to which it can be reduced by the waste heat recovery unit. As a good rule of thumb, assume that Tout will be about 100F above the lowest temperature process consumer you have aviable to heat. As an example, if you have an exhuast stack waste heat source with a maximum exhuast tempreature of 650F and your conusmer is a boiler feedwater preheater with an outlet tempreature requirement of 250F, assume that you can reduce the temperature of your exhaust to no more than 350F (Tout – 350F).

Contact our experts to determine the amount of waste heat in your processes and suggest the best waste heat recovery system to maximize the processes’s efficiency.

What Is Industrial Waste Heat?

Many industrial processes emit large amounts of waste heat that is underutilized or overlooked entirely. Industrial processes with a waste gas stream over 350°F (typically exhaust gas) are often considered industrial waste heat because the heat energy is wasted and released into the environment. Sources of waste heat include heat loss through conduction, convection, and radiation of industrial equipment and heat released from combustion processes. The heat loss of industrial processes can be categorized as high temperature, medium temperature, or low temperature.

Learn More About Waste Heat Recovery Systems

Industrial heat waste recovery technology provides a sustainable option for industrial processes, helping to reduce plants’ dependence on expensive fossil fuels. Reusing heat waste is a simple way to reduce overall energy consumption and reduce a plant’s carbon footprint. With the various waste heat recovery system types available, it’s important to partner with a knowledgeable supplier of industrial waste heat recovery systems to maximize the efficiency of your processes and reduce your energy costs.

Sigma Thermal has a team of heat energy management experts to provide industries with cost-effective waste heat recovery systems. Our engineers are continually improving our heating systems and providing energy audits and/or technical consulting to determine if customers have heat waste energy to recover and ensure they have the most cost-effective operation possible. If our audit shows benefits for heat waste recovery equipment, we offer the right equipment to guarantee energy savings to ensure your heat recovery potential is fully realized.

Request a quote to learn how your company can benefit from heat recovery equipment and how our heat energy recovery experts can assist with choosing the best system for your needs.

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