Over the years, Sad-Chemie has continued to optimize the efficiency of the steam-injection process. Steam-injection assemblies were replaced with steam ejectors that not only treat the clay, but also serve to pump the clay slurry between tanks. Clay solids were increased to reduce the steam cost per pound of product. The solids increase was initiated after research scientists at the company demonstrated that benefits derived from steam ejection are independent, within a moderate range, of solids concentration.
Sad-Chemie's first steam ejectors often were disabled by stress fractures caused by excessive vibration. The company eliminated these by improving steam-ejector manifold design and the start-up procedure. Modifications to the manifold design included flex joints at key points and the elimination of sharp bends in the piping.
Sad-Chemie improved the start-up by establishing a method to minimize pressure at the ejector-system discharge end. The rate of steam flow is increased gradually at start-up with the manifold discharge valves completely open. This procedure prevents shock effects as the hot steam first comes into contact with the relatively cold ejectors and associated piping. After the ejectors and associated piping reach a steady temperature, the steam flow then is increased quickly to the desired flow rate.
Steam delaminates the clay, increasing the number of clay platelets available for cation exchange during the coagulation step. Organoclay performance is enhanced as the steam increases the clay hydration, making the clay more dispersible and reactive. Increased clay hydration can result from cavitation effects as high-energy molecular collisions and rapid contraction-and-expansion transitions take place within the steam ejectors.
Organoclay performance can be enhanced significantly through the use of a single steam-ejection stage. A recommended steam-to-clay ratio is approximately 1.5. Higher-performance products can be created through the use of two steaming stages. Many people believe higher-performance products also benefit from a holding time of about 40 minutes to 80 minutes between the two stages.
Temperature greatly affects the performance of steam ejectors. If the slurry temperature is too high, vacuum suction will decrease significantly, and severe process vibration could result. If the slurry temperature is too low, the steam-to-clay ratio will not be high enough to bring about beneficial effects.
Cleaned and Steamed
Techniques such as steam injection optimize the dispersion of the clay platelets to enhance reaction efficiency.
What will it cost?
A typical steam ejection system used at Sad-Chemie is equipped with three ejectors made from stainless steel, six flex elements (two per ejector to allow for proper movement), a vortex meter for measuring steam flow rate, various valves and a flanged header. The header is made with smoothly curved piping.
This design helps to minimize pressure drop and system vibration. Construction costs for a well-designed steam ejector system typically range from $7,500 to $10,000, depending on specific process requirements.
Drucker is plant manager and Mattingly is senior research chemist for Sad-Chemie Inc.'s Performance Additives Div. in Louisville, Ky. Contact them at firstname.lastname@example.org and email@example.com, respectively.