By Robynn Andracsek, P.E., Burns & McDonnell and Contributing Editor and Minda Nelson, P.E., Burns & McDonnell
One of the first commercial power plants in the U.S. was Thomas Edison’s Pearl Street Station. This combined heat and power (CHP) plant was in lower Manhattan and was roughly 50 percent efficient. However, in 1882, Mr. Edison was likely fixated on providing a reliable source of power to illuminate his light bulbs rather than clean and efficient energy. Electricity generation began with independent systems and moved over time to the other extreme, an interconnected national grid. As with most issues, the pendulum eventually swings back, as shown by the recent surge in popularity of local CHP plants.
CHP is an efficient, clean and reliable approach to generating power and thermal energy. In most cases, CHP captures the main by-product, heat, for industrial heating purposes. Typical facilities that utilize on-site CHP are manufacturers, universities, hospitals and other large institutions. Today, power generation is slowly returning to its early roots: on-site power doubling as a source of energy and heat/steam generation.
The benefits of CHP are numerous. Reliability and the location of generation plants are becoming a concern as air regulations become more stringent and cause plants to shut down. When a plant is shut down, especially in urban areas, there is a struggle to add replacement transmission capacity to bring power back into the area. When planning an on-site CHP project, the proximity of the project to existing generation and transmission infrastructure can take a lower priority. In the initial stages of a green-field project, location plays a role as transmission lines, supply and demand and availability of power from the grid are factored in. In some cases it can increase the timeline of the project due to lack of transmission capacity. On-site CHP projects can by-pass these planning hurdles.
From a permitting point of view, CHPs tend to face less opposition from environmental groups than permitting the standard fossil fuel-fired power plant. CHPs are still subject to the typical air regulations, such as non-attainment New Source Review (NSR) and Prevention of Significant Deterioration (PSD). But if a project can stay below major source thresholds, it can reap the benefits regulations specifically enacted to encourage high efficiency generation. One such example is Texas’s “Standard Permit for Electric Generating Units,” which provides simple and quick permitting track for plants meeting lb/MWh limitations and heat recovery minimums.
On-site CHP projects located in urban areas and subject to PSD may pose a challenge as they compete for available increment in the area, comply with the National Ambient Air Quality Standards (NAAQS) and address non-attainment issues. Care must be taken to ensure that the relatively short smoke stacks from these generators can meet the new one-hour NAAQS for NOX and SO2.
The benefits of on-site CHP can be seen at Thermal Energy Corp.’s (TECO) on-site CHP plant. Completed in 2010, this plant provides power to the Texas Medical Center Campus in Houston, among the largest medical centers in the world. When the master plan is fully implemented, the plant will feature additions of 100 MW of on-site power generation, 80,000 tons of chilled water, 152,000 ton-hours of chilled water storage and 540,000 pounds-per-hour of heat recovery steam generation. (See Managing the Plant, page 20.)
The master plan objectives of the TECO on-site CHP project were to improve efficiency and reliability and meet the load growth of the expanding medical campus, while significantly reducing air emissions. On-site CHP systems have significantly higher electric and thermal efficiency. Prior to installing the CHP system, the TECO plant was operating at 40 percent efficiency. Today the plant boasts an efficiency of 80 percent. In comparison, large scale utilities typically have efficiencies of approximately 35 percent. Environmentally, the new CHP project reduced fossil fuel consumption by 61 percent. The Houston area, a severe ozone non-attainment area, benefits from the reduction of regional air pollutants. The medical center benefits from assurance of a steadfast power supply; the Texas Medical Center serves a critical mission and cannot afford to lose power. During hurricane events, TECO is able to provide uninterrupted service to every doctor and patient.
Renewable power generation (solar, wind) is politically popular. However, the public has yet to grasp that a stable transmission grid depends upon a consistent power supply to meet base load needs. With today’s focus on clean energy, on-site CHP is a viable option for facilities that want more control over their power operations, improved efficiency and lower air emissions.
Power Engineerng Issue Archives