You can't pick that famous low-hanging fruit if you can't find the tree. So, to help users find some tasty savings in their often complex and sometimes forest-like applications and facilities, ABB Power Generation North America offers some very thorough energy assessments and audits.
For instance, ABB recently helped a 400 MW, coal-fired power plant identify 47 different opportunities that could save it $4 million to $11 million per year, if all the recommended projects are carried out, according to Rich Vesel, global product manager of ABB's electrical balance of plant (eBOP) program for energy efficiency. Individual identified savings ranged from the smallest at about $5,000 up to a couple that were about $2 million each.
For example, this particular audit was finished in July 2010, and found several previously unidentified leaks in the plant's blowdown valves that were increasing its blowdown rate from 3% to 7%. This was a significant drain on the facility's revenue, Vesel said, and also on its material resources.
"This assessment was done at a coal-fired plant, but the theory, methods and benefits of performing these audits are universal," Vesel said. "And doing them is even more important since the U.S. EPA began requiring in February 2010 that anything that emits more than 75,000 tons of carbon dioxide per year must perform an energy assessment—except for utilities, which are exempt."
"We have a lot of aging plants nationwide that are 30, 40 and 50 years old, and their plant—net and gross—heat rates are gradually deteriorating, and so their costs are going up," Vesel explained. "There's also been a moratorium on new coal plant construction, and the EPA also announced in November 2010 that it's requiring that Best Available Control Technology (BACT) be applied to plants for energy efficiency improvement."
Typical opportunities in an average 400 MW, fossil-fired boiler unit from the 1970s include:
- Identify and correct leaks, cycle isolation and operability issues.
- Apply new motors and variable-frequency drives to (VFDs) to the largest pumps and fans.
- Apply advanced controls to O2, spray flows and controllability issues.
- Reduce house load of 25 MW to less than 20 MW.
- Improve net heat rate by more than 3% on average.
- Improve capacity by more than 6-12 MW at full output.
- Analyze against unit load, cost and sale profiles, using above improvements.
- Gain per-megawatt savings of $500,000 or more per year in additional capacity.
- Achieve conservative spectrum of project payback from less than six months to up to five years.
In the case of the specific coal-fired plant, ABB first examined its 40-year-old "boiler island" section and then its "turbine island" section. This involves a three-phase process, including 1) identifying savings and improvement opportunities, 2) compiling a prioritized energy management master plan, and 3) implementing, commissioning and sustaining projects recommended in the plan.
Once the original 47 improvements and savings opportunities were found, ABB helped the plant decide which five or 10 to do first based on the investment required, how quickly they could be done, and how big a savings they could generate.
ABB's audits are thorough because they extract and analyze longer-term operations data, Vesel added. "We'll check a plant's PI software historian for a year's worth of data, and this will show trends that don't appear in an application's usual thermal models. Controllable losses can account for 50% of the difference between how a plant is performing and how its engineers and manager would like it to be performing."