Saint-Gobain Corporation: Vancouver Impact Mill Heat Recovery | Saint-Gobain Corporation
“This heat recovery project allowed the plant to reduce natural gas consumption by 4.5 percent and reduced GHG emissions by 865 tons per year. The energy reduction is excellent progress and exceeded the company’s internal goals for energy reduction. In addition, the added safety improvements are a plus.”
--Energy Manager Today Awards judge
Saint-Gobain Corporation’s manufacturing plant in Vancouver, British Columbia, Canada produces gypsum wallboard. The process utilizes two Impact Mills to produce an intermediate product called stucco. Stucco is produced by simultaneously heating and grinding gypsum rock. The stucco is then pneumatically conveyed through a cyclone and dust collector. Previously, the mills operated in a single pass system, where ambient “traveling air” was drawn into the burner chamber, heated between 600-720 degrees centigrade and exhausted at 150 degrees centigrade. This method was inefficient because thermal energy was lost by exhausting humid, preheated travelling air and electrical energy was wasted using inefficient fixed speed fans and dampers to draw air through the system.
The plant made use of financial incentives offered by local Natural Gas and Electrical utilities for a heat recovery project. Feasibility reports were developed by consultants to evaluate and design the improvements. The project improved efficiency by: Installing recirculation ducting to capture a portion of the heated exhaust stream and return it to the burner; replacing inefficient system fans and dampers with new fans on variable frequency drives.
Process measurements were input into heat and energy models to estimate potential natural gas savings from the project. The models showed that returning hot, moist air instead of cold ambient air to the system would significantly reduce the energy required to create the stucco.
The heat recovery project reduced plant gas consumption by 4.5 percent, exceeding Saint-Gobain internal energy reduction goals. This is projected to reduce the plant’s annual CO2 emissions by 865 tons. Additionally, the projected reductions in CO2 emissions from fan efficiency improvements total 14,700 kilograms annually. These energy savings, along with the incentives available from the utility companies, resulted in an ROI of 1.19 years.
Other unique process improvements were also made possible as a result of this project. Stucco quality has improved and become more stable by returning humid air to the system. The re-circulation loop allows the process to run consistently at a higher humidity levels than before the installation.
Safety improvements were also implemented as part of the heat recovery project. Emergency air dampers were installed and programmed to open and allow cool air to enter the piping in case of temperature extremes. Modulating dampers on the exhaust line and burner pressure sensors were also installed to ensure that the burner chamber never expels hot air into the plant.