System economizes use of carbon dioxide to lower process water pH, TSS
- Published: Monday, 16 January 2012 14:16
- Written by CP Staff
“We have a unique way of mixing carbon dioxide gas into flowing water, where gas bubbles convert to carbonic acid and lower the pH,” says Fortrans CEO Bob Cooke. “Water from concrete plants too easily fouls the diffusers or sparger assemblies producers have traditionally tried for imparting carbon dioxide gas into high pH water.”
Conventional, clog-prone diffusers mimic the sieve-like, layered-screen design of faucet aerators, he adds. Injecting CO2 through such devices in ready mixed or precast concrete plants tends to yield a gas utilization rate of about 20 percent. At that efficiency, CO2 becomes a tough sell against sulfuric or hydrochloric acid—even in the face of handling concerns with caustic compounds.
Fortrans’ new diffuser and injection equipment exhibits up to 90 percent gas utilization, measured by the rate of CO2 conversion to pH-lowering carbonic acid before bubbles rise to the surface. Carbonic acid lowers pH by converting suspended solids into calcium and magnesium carbonates; that process, in turn, lowers the water’s total suspended solids content to dischargeable levels.
Fortrans’ concrete-grade 5000 Series models (B, S, SK) are set to lower treated process water to a) 7.5 pH, versus the Environmental Protection Agency’s 9.0 pH threshold for release from the plant property; and, b) total suspended solids to the 14–17 range against the EPA’s <30 threshold. Prior to the new diffusion and injection chamber, Fortrans equipment operated at about 75–80 percent CO2 utilization efficiency, but had limited capacity.
The patent-pending chamber consists of a CO2 gas-charged cylinder housing diffuser material, and rests above the flow of water drawn from the concrete plant’s cleanest detention basin or final weir. It is engineered so that only diffused gas goes into the water, from which the chamber remains free of contact.
An existing Fortrans system might require 10 hours to bring 30,000 gallons of high-alkaline water to a 7.5 pH. With greatly improved capacity, the new technology can treat a similar quantity of water in two hours. Bearing on 10-ft. square slabs, the 5000 Series models are equipped with a programmable logic controller pre-set to maintain a 7.5 pH for treated process water used in plant and fleet operations, or discharged according to permit guidelines at storage capacity peaks.
The Fortrans system circulates the water with a submersible pump in a closed-loop piping system, continually monitoring pH level. When the pH rises to 8.25, the PLC actuates a solenoid valve and begins to diffuse and inject CO2 gas. Once the 7.5 pH level is attained, the valve shuts off and the water circulates until the pH reaches 8.25. Product engineers strongly recommend producers run the equipment in continuous versus batch mode. Continuous treatment optimizes CO2 use due to the buffering effect a mass of treated 7.5 pH water has on incoming flow of higher alkaline water. Batch mode will almost always consume more CO2 than the continuous treatment method.
Carbon dioxide costs about $.29/lb. delivered, Fortrans notes. If treating 30,000 gallons per day, a concrete producer will use about 100–200 lbs./week, at a cost of $30–$60. The figure will vary depending on total alkalinity of the process water. Fortrans estimates a 60–70 percent cost savings for plants using the 5000 Series versus hydrochloric acid-based pH neutralization systems, and up to 80 percent less than those using granular sodium bisulfate. — Fortrans Inc., 866/958-7267; www.fortransinc.com
Bibko NA, Fortrans ink distribution agreement
Cedar Falls, Iowa-based concrete reclaiming equipment specialist Bibko North America LLC has become the exclusive North American representative of Fortrans Model 5000 pH control systems.
Effective January 2012 and covering all 50 states and territories plus Canada, a late-December distribution agreement ensures that North American customers will now receive the full attention and support of Bibko’s dealer network. Dealer staff will be available to travel to the customer’s site, help with equipment selection and installation, and do follow-up service calls.
“Fortrans pH control systems are a perfect fit with our array of products and services for concrete and process water reclaiming and recycling,” said Bibko NA Director of Marketing and Sales Owen Blevins. “Concrete producers have long struggled with the proper disposal of concrete process water, which is highly alkaline. The Model 5000 line directly addresses that problem with safe, acid-free carbon dioxide injection and diffusion.”
With precise monitoring and control of alkalinity in pit systems, settling basins, lagoons and other containment areas, Fortrans 5000 Series models reduce potable water usage by producing water ideal for recycling, rinsing trucks, dust control or irrigation. Their simple, low-maintenance design makes them safer and 60–70 percent less costly to operate than acid-based systems.
Bibko NA website, www.concreterclaiming.com, provides education, tools and resources about concrete reclaiming and water recycling, as well as product information. Bibko GmbH in Beilstein, Germany, manufactures systems that provide a complete, zero-waste solution to the problem of waste concrete and washout water disposal by recovering aggregates and cementitious water for use in the production of new concrete. — www.bibko.com