Combined Heat and Power (CHP) is steadily gaining ground in North America. Its installed capacity in the U.S. is now more than 80 GW. This represents more than 4,600 facilities and 7% of the US’s total electric generating capacity. But a better way to look at it is that CHP represents 13% of manufacturing capacity. In other words, CHP powers more than an eighth of all the power needed for the entire manufacturing sector.
Natural gas is the primary fuel source. Three out of four CHP plants are driven by natural gas. Biomass, biogas, and waste account for another 15%.
CHP’s overall popularity is all about efficiency. According to the U.S. Department of Energy (DOE), the average efficiency of fossil-fueled power plants in the United States is 36%. By recovering and using heat from on-site electricity production, CHP systems typically achieve total system efficiencies of 65% to 80%. Some approach 90%.
Take the case of the Eight Flags CHP plant in Florida’s Amelia Island. It provides steam and other services to a Rayonier Advanced Materials Inc. (RYAM) manufacturing facility. Florida Public Utilities (FPU – part of Chesapeake Utilities Corp.) gains the power for its customers in the local area.
“The plant would not have been possible without the tight artnership between the local grid authority, FPU, and the industrial customer RYAM as well as vendors such as Solar and Rentech,” said Mark Cutshaw, Manager, Electric Operations, FPU.
A Solar Titan 250 gas turbine powers the plant, providing more than 20 MW. NOx is maintained at less than 15 ppm and CO2 at less than 25 ppm at 15% O2. Solar has a long-term service agreement (LTSA) and takes care of the major inspections and maintenance actions.
An HRSG from Rentech Boiler Systems feeds steam to RYAM at 160 psi and 420°F. It recovers around 70-75,000 pounds of steam per hour and has the capability to increase that amount using duct burners that add 125,000 pounds per hour of process steam for a grand total of 200,000 pounds per hour if needed.
Demineralized water provided by RYAM is channeled through a hot water economizer in the Rentech HRSG to increase the water temperature by 70°F. This heated demineralized water is sent back to RYAM for use in production processes, saving the company from having to generate its own power to heat the water. This also helps RYAM to keep emissions low. Exhaust heat is also used to heat feedwater before it is sent into the HRSG. Effective use of waste heat raises overall efficiency at Eight Flags to 80%.
An inspection is scheduled every two years to ensure the HRSG is operating within specifications. Vibration levels are regularly checked and onsite personnel inspect the air and water side of the HRSG as well as the integrity of the tubes to see if they are losing any material.
“In almost 10 years, we have hardly lost any tubes and have had minimal issues with the Rentech HRSG,” said Cutshaw. “The key to smooth HRSG operation is to have a good HRSG from a reliable vendor and then make sure that water treatment is done well so water quality remains very high.”
The RYAM plant pays for the steam generated from Eight Flags and occasionally purchases power from FPU. The utility sells almost all the electricity from the CHP plant to other customers.
With Eight Flags CHP on site, RYAM can take one of its own boilers down for maintenance and still gain enough steam from the HRSG and duct burners to satisfy its needs.
On the business side, everyone is happy at the midpoint of a 20-year contract. It is expected that the agreement will continue once the 20 years are up as the economics work out well for all concerned. Power, steam and hot water are always available.
“If the mill has a hiccup on power or steam production, Eight Flags acts as a backstop so RYAM can continue to make more cellulose products,” said Cutshaw. “If they need more steam, we can get the duct burners in the HRSG up and running within 10 mins. That boosts team from 75,000 to 200,000 per hour if the facility needs it.”
This is just one example of a CHP arrangement between a power plant, a utility, and a manufacturing customer. There are many more successes like this across North America. They benefit from a reliable source of energy (onsite or adjacent) without being dependent on the grid or subject to potential rate increases as a utility customer. When the economics are viewed across a twenty-year span, CHP often makes financial sense to all parties concerned.
