Published: February 6, 2014
- BENEFITS & BARRIERS
- CASE STUDIES
Capture and reuse waste heat to save money and energy
Heat recovery is a means of transferring energy that is typically wasted in a building or manufacturing process to other productive end-uses. The heat loss from these processes may be intentional (such as in air conditioning processes, where heat needs to be rejected for the system to work), incidental (such as in a compressed air system where heat is lost through the process of compression) or accidental (such as heat lost through the envelope of a building). There are mature technologies for recovering waste heat for most building systems and from industrial processes. Newer to the market are technologies for capturing low-temperature waste heat.
There are large quantities of industrial waste heat in the 100 – 400° F temperature range. For example, gas from industrial boilers with recovery technologies exhausts at temperatures between 300-350° F. Cooling the flue gas below the usual temperature limits of 250-300° F can significantly increase heat recovery by recovering the latent heat of vaporization.
Cool exhaust gas to 150-160° F. Various designs are used to ensure that they withstand the acidic condensate that is deposited as a result of the water vapor contained in the exhaust gas condensing as it cools.
Indirect contact condensation recovery
Cool gases to 100-110° F at which temperatures the water vapor in gases will condense almost completely. Flue gas passes through a tubular heat exchanger and the water does not come in contact with the flue gases.
Direct contact condensation recovery
The flue gas and cooling liquid are mixed directly and do not involve a separating wall across which the heat must be transferred. Heat is recovered in a spray chamber where the flue gas comes in contact with cool liquid droplets.
Transport membrane condenser
Water (and its latent heat) is extracted from the flue gas at temperatures above dew point using capillary condensation and recycled into the boiler feedwater.
Steam is used in many industrial processes. Chemical manufacturers, refineries, food processors, paper manufacturers and primary metal industries consume the most fuel for steam generation where it can account for between 10 to 80% of their energy consumption. Unrecovered heat from industrial boiler exhaust gases is estimated to be about 1,200 TBtu/yr—most of which is low temperature heat.
Things to consider when choosing flue economizer heat recovery options
Each system and process should be considered with the expertise of an engineering specialist, since each project is unique and has specific constraints and challenges. That said, there are a number of general points to think about when considering heat recovery options.
Capacity factor of the system
Generally, the economics of boiler heat recovery is more appealing for boilers with longer run-times and high capacity factors. For those boilers that run more intermittently, the cost of installing the system may not be recouped by the amount of energy saved.
Typically, oxygen levels should be greater than 3% for an effective heat recovery system.
Amount of make-up water
Economics are more favorable when the waste energy is used to heat feed water with high levels of make-up water.
The additional heat recovery equipment will require additional space. This may present an issue if space constraints exist.
Man-power for operation
Heat recovery options require added operational time and maintenance compared to conventional operations. This should be considered when analyzing heat recovery options.
Potential for significant savings: potential heat recovery is dependent on a number of factors, but under an example scenario, the U.S. Department of Energy estimated the value of annual energy recovered from retrofitting a 100,000 lb/hr steam boiler with an indirect contact condensing economizer to be $582,170.
Challenges and market barriers
Cost: the cost of the equipment, auxiliary systems and design services can lead to long payback periods.
Economies of scale: first-cost of equipment favors large scale operations and presents challenges for smaller manufacturers.
Lack of end-use for recovered heat: many facilities may not have an on-site use for the recovered heat.
Statewide energy savings
We took a high-level look at the potential energy savings in Wisconsin from advanced heat recovery technologies, like the Ultramizer. The estimate is meant to provide a sense of scale showing the impact this technology might have on Wisconsin energy customers.
To estimate statewide impacts, we assumed that this would be a retrofit opportunity to install Ultramizer technology for process heating in industrial applications. We applied a technical savings rate of 15% to the process heating consumption. We assumed an applicability rate of 50% of industrial applications.
All data used for these estimates are from the Wisconsin Energy Statistics (2012) and Department of Energy's Manufacturing Energy Consumption Survey data (2010).
There are not currently financial incentives available for the Ultramizer technologies specifically. However, Focus on Energy offers custom incentives for Large Energy User (with average peak monthly demand greater than 1000 kW) and heat recovery systems may be applicable under that program. https://focusonenergy.com/sites/default/files/ServicesandIncentivesComme...
Cannon Boiler Works Ultramizer
The Gas Technology Institute (GTI) partnered with Cannon Boiler Works to develop the Ultramizer, which is a transport membrane condensing flue heat recovery system. The heat recovery systems transfers both sensible and latent heat, and can increase boiler efficiency up to 95%. There are other non-boiler applications for which heat and water can be recovered using this technology.
The Ultramizer uses both indirect and direct contact condensation recovery methods (see "Applications" for more details on these types of systems) to recover heat and hot water effectively.
The Ultramizer technology can cost approximately 20-50% more than typical conventional condensing economizers, but owners can expect to see an increase of efficiency in 2-5%, which translates to significant savings over the life of the system. GTI and CBW expect that the installed systems would see a 2-3 year payback.
This system is commercially available but has been installed in less than a dozen sites.
Considerations When Selecting a Condensing Economizer
summary: This tip sheet written by the Advanced Manufacturing Office arm of the Department of Energy provides insight into what to consider if thinking about fuel economizers for steam boilers. The information includes details on the main two types of condensing economizers, indirect contact and direct contact, and provides suggested actions for deciding if retrofitting with an economizer is right for your situation.
citation: Department of Energy (2012) "Considerations When Selecting a Condensing Economizer - Steam Tip Sheet #26B." Accessed May 4, 2014.
more Steam Tip Sheets from DOE can be found here: http://www1.eere.energy.gov/manufacturing/tech_assistance/steam.html
Waste Heat Recovery: Technology and Opportunities in U.S. Industry
summary: The study provides an overview of industrial waste energy heat recovery technologies, particularly focusing on the research and development needs to improve these technologies. The study applies a bottom-up approach, analyzing waste heat quantity, quality, recovery practices, and technology barriers. The two main areas of additional research the authors believe is need in industrial waste heat is to extend the range of existing technologies to increase economic effectiveness and seek out new methods and technologies for heat recovery, especially for unconventional waste sources.
citation: Department of Energy, Industrial Technologies Program (2008). "Waste Heat Recovery: Technology and Opportunities in U.S. Industry." Prepared by BCS, Incorporated. Accessed May 4, 2014.
Install Waste Heat Recovery Systems for Fuel-Fired Furnaces
summary: This Process Heating Tip Sheet briefly summarizes waste heat recovery systems for fuel-fired furnaces. The tip sheet discusses the benefits of installing a heat recovery systems and provides an overview of the common heat recovery applications, including preheating combustion air, steam generation and water heating, and load preheating.
citation: Department of Energy, Industrial Technologies Program. (2005) "Install Waste Heat Recovery Systems for Fuel-Fired Furnaces." Accessed May 4, 2014.
BUILDING DESIGN / ENVELOPE
HEATING / COOLING