Jake received a call from one of the plants for which he was responsible. The plant’s engineers had just conducted an energy conservation survey and one of the items high on the list of ideas to consider was condensate recovery; they wondered if Jake would help them evaluate its feasibility.
Jake had conducted many energy conservation surveys in his career and condensate recovery often came up. Depending on the plant, it could be a money-making-or-saving move. But, in some cases, depending on the age and the type of equipment used on the site, it could be a dead-end evaluation. Jake prepared to visit the plant to help with the evaluation.
The plant was one of the older ones on Jake’s list. It had been built when energy was inexpensive, reciprocating steam engines were the predominant power source, and the primary purpose was production. It also had been built in a hurry; the window for the products was fairly short. As a result, the designers had ignored many energy-saving features.
Elaine met Jack at the gate with the enthusiasm Jake would expect from a young engineer. She had been in charge of the survey and developed a number of excellent ideas for energy savings. Many already had been implemented, with the plant reaping energy and cash savings. However, management resisted when Elaine introduced the idea to recover condensate. Many objections centered on the cost of putting in a piping system to recover the liquid. Others concerned the quality and suitability of using a “dirty” stream.
Elaine already had split the plant into target zones and surveyed how much condensate was available in each zone. She had narrowed her work down to one area with the most condensate available. She identified the streams based on saturation temperatures to enable quick determination of the streams’ heat content. She asked Jake what to do next.
Jake said, “The first thing to do is determine if there is a need for the heat content in the condensate. We can survey the heat sinks in the process area to see if we can displace some primary steam.” Elaine and Jake reviewed the process diagrams and quickly discovered several low-temperature inputs that currently were heated with high-temperature and high-pressure steam. Jake noted that because the plant was built fast, the designers would have minimized the numbers of levels of steam coming in to the area and used the available high-pressure steam. Elaine analyzed each potential application and noted two worth further evaluation.
The evaluation showed the condensate heat recovery was financially justified, so, Elaine set about developing a project to install two new heat exchangers to capture the savings. The area was able to save about $30,000 for each stream and the project had approximately 30% return on investment. Energy savings are usually small incremental steps as this example showed.
Elaine also asked Jake about recovering the condensate liquid and sending it back to the central powerhouse to displace some of the high-pressure boiler makeup water. Jake indicated they would have to do some chemical analysis of the condensate first. The area Elaine first targeted previously had contained steam-engine-driven process compressors. Most of these had been replaced with electric motor and steam turbine drives. Elaine arranged to have condensate samples collected from various point sources in the process area. The condensate would have to meet very high purity standards due to the stringent feedwater requirements for the site’s high-pressure boilers.
Elaine had the lab analyze the condensate for high oil content, pH, carbonic acid and the other usual water analyses. Unfortunately, the residual oil in the system precluded the use of this process area’s condensate for feedwater makeup. Elaine next evaluated whether the condensate could be used as make up to the area’s large cooling towers. This proved feasible and a line was run to the cooling tower. (For details about cooling tower fill, see “Understand the Importance of Correct Cooling Tower Fill”).
Elaine then started evaluating other areas to see which were candidates for condensate reuse. All in all, Elaine identified nearly $200,000 per year in site energy and water savings.
Have you looked around your site for condensate that could be put to good use? Make sure it meets the requirements of your equipment before dumping it into makeup streams. Happy energy hunting!
Earl M. Clark, PE, – Engineering Manager, Global Energy Services. Clark retired from DuPont after a career of 39 years and 11 months and joined Hudson’s Global Energy Systems Group as Engineering Manager. During his over 43 years in the industry, he has worked in nearly all aspects of the energy field; building, operating and troubleshooting energy facilities for DuPont. He began his energy career with Duke Power and Clemson University during the energy crisis in the 1970s.
Active in both, the American Society of Mechanical Engineers and the American Society of Heating, Ventilating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), Clark was chairman of ASHRAE's task group on Halocarbon Emissions and served on the committee that created ASHRAE SPG3 - Guideline for Reducing Halocarbon Emissions. He has written numerous papers on CFC alternatives and retrofitting CFC chillers. He was awarded a U.S. patent on a method for reducing emissions from refrigeration equipment. He has served as technical resource for several others.