EnerTech and its engineering partner HDR have designed a 675 wet tons per day SlurryCarbTM facility in Rialto, CA. The facility is being constructed adjacent to the City of Rialto wastewater treatment plant.
Click here to enlarge imageEnerTech’s process chemically converts biosolids into a fuel that can be used in most coal-burning facilities. Using heat and pressure, the process carbonizes the organic matter in biosolids and ruptures cell walls to release bound water. The resulting slurry dewaters to 50% total solids by centrifugation, and is then dried using approximately two-thirds less energy than conventional drying. The energy savings result in approximately a one-third reduction in overall cost compared to traditional drying technologies.
The SlurryCarbTM process consists of seven basic steps, described below:
Step 1 - Biosolids Preparation
Biosolids at 20-30% by weight solids are received from various wastewater treatment plants. The feedstock is then macerated until all particles are less than ½ inch in diameter.
Step 2 - Slurry Pressurization
The prepared biosolids are slurried and pressurized above the vapor pressure of water at the desired reaction temperature. Pressurization prevents the water from boiling during reaction and ensures that the carbonization reactions occur in liquid phase.
Step 3 - Slurry Heating
Specially designed heat exchangers raise the temperature of the slurry to the range of 400-550oF.
Step 4 - Reaction
The cellular structure of the biosolids ruptures (lysis) and the carboxyl groups (-C-O-O) of the organic molecules break off and are released as carbon dioxide gas in a reaction known as decarboxylation. This reaction causes the biosolids to become hydrophobic. The reaction is stopped short of pyrolysis.
Step 5 - Dewatering/Drying
After partial cooling and depressurization, the carbonized slurry is dewatered via centrifugation to about 50% by weight total solids. The dewatered slurry is then dried to 90+% total solids. This final product, called E-Fuel, is a renewable fuel with a heating value of approximately 7,000 Btu/lb.
Step 6 - Filtrate Processing and Recycle
The centrifuge centrate and dryer condensate are further processed to remove contaminants in a wastewater treatment step. The resulting effluent is discharged with a portion being recycled back to points in the process where it can be used.
Step 7 - Utilization
The renewable E-Fuel is used as an alternative to fossil fuels. E-Fuel can be used in most coal-burning facilities with little or no modification to the facility’s existing equipment.
E-Fuel
The end product of the SlurryCarbTM process, E-Fuel has been certified as a renewable fuel by the California Energy Commission and the Green-e Renewable Electricity Certification Program and can be used as a renewable alternative to fossil fuels.