The project objective is to study the feasibility and cost/benefit of recovering heat energy from diesel exhaust and turbocharged air for rural Alaskan villages, which use diesel generators for power generation. The project entails selecting the most appropriate heat recovery application for the type of diesel generators used in rural Alaskan villages, design of experimental exhaust and after-cooler heat recovery systems for testing, feasibility study, and economic analysis, and the choice of a village diesel generator for field demonstration.

University of Alaska, Fairbanks, AK
Alaska Village Energy Corporation, Anchorage, AK

In rural Alaska, there are nearly 200 villages consuming about 400 Million kWh of electricity per year. If the waste heat in the exhaust and turbocharged air were put to appropriate use, there would be a significant fuel savings.

Results 
The heat recovery application has been determined based on the need and potential benefit. Selected applications include two different types of space heating and community water loop heating.

An experimental exhaust heat recovery system has been designed, installed, and instrumented. Test results have been obtained from 350 hours of system operation. Based on the experimental data, analysis has been conducted and the following preliminary conclusions have been obtained:

• An exhaust heat recovery system for heating application is feasible, which is supported by these observed facts:
  • The heat recovery system showed no unfavorable effect on engine performance (e.g., exhaust back pressure).
  • The heat recovery system showed very consistent performance for the 350-hour system operation (i.e., consistent pressure, temperature, and efficiency data).
  • Heat exchanger efficiency was around 80 percent and steady.
  • The heat recovered per unit of electrical energy consumed is not very sensitive (i.e., less than 10 percent difference in efficiency) to engine load (for a load between 50 percent and 100 percent of rated load).
  • About 1.5 percent, or 150 g, of exhaust soot was deposited in the heat exchanger. (According to the literature, deposited soot reaches an asymptotic level over long-term operation). The amount of soot deposited inside the heat exchanger after 350 hours of operation showed no sign that it would affect the regular maintenance schedule (i.e., an extremely thin layer of soot on the heat transfer surface.). The soot deposited was easy to clean (using compressed air and a brush).
  • No trace of corrosion in the heat exchanger was observed.
  • Operation procedure of the heat recovery system was simple (i.e., turn on/off the pump and open/close valves).
• The economic benefit of the exhaust heat recovery system is desirable (based on the data obtained from this experiment):
  • In terms of amount of fuel, the amount of heat recovered is equivalent to 1.2 gallons of fuel for every 100 kWh of electrical energy consumed (or $3/100 kWh, assuming fuel cost = $2.50/gallon).
  • For 100 percent heat usage, the estimated breakeven point for this exhaust heat recovery system is less than 2.5 years. (This analysis includes fuel cost of $2.50/gallon, capital cost of $40,000, maintenance cost of $2,000/year, a 10 percent compound interest rate, and an average of 70 percent engine load. Operation cost was not included due to the short heat transmission pipeline or negligible pumping energy cost.) For 80 percent heat usage, the estimated breakeven point is 3.3 years. Breakeven point largely depends on the percentage of heat usage (or energy loss of the system).
  • Assuming a heat recovery system can last for 10 years and there is 100 percent heat usage, the system can then recover the amount of heat equivalent to $3/100 kWh of consumed electrical energy (or more than $20,000/year at a 70 percent engine load) for 7 years.

Benefits 
Besides the potential of gaining significant fuel savings and the associated economic benefits, application of exhaust heat recovery may also reduce emissions of greenhouse gases. The potential benefit obtained from applying an exhaust heat recovery system is case-dependent. Influential factors may include distance between engine room and area to serve, equipment shipping cost, local fuel cost, etc.

Summary 
According to the experimental data obtained from 350 hours of operation of the exhaust heat recovery system, the tentative conclusion is that applying exhaust heat recovery for heating is feasible and beneficial. To further confirm this conclusion, more test data and further investigation are recommended. Currently, researchers are undertaking more data collection and analysis for the exhaust heat recovery system, development of the design specification of a turbocharger air heat recovery system, and preparing a final report.

(February 2008) 
The project is completed. The final project report is listed below under "Additional Information".

Funding 
This project was awarded under DOE solicitation number DE-FC28-01NT41248.

$305,110

$67,124 (22% of total)

NETL – Purna Halder (Purna.Halder@NETL.DOE.Gov 918-699-2084)
U. of Alaska Fairbanks – Chuen-Sen Lin (ffcl@uaf.edu or 907-474-5126)