Direct-contact steam injection lends itself to many applications, including water heating, pulp and paper-stock bleaching, starch cooking and some specialty applications. In these and other applications, there are multiple advantages to using direct-contact steam injection for process and utility heating. These benefits are realized by an internally modulated system that provides the following characteristics to a steam-heating process: energy efficiency, precise temperature control, instant temperature rise, smaller footprint, less maintenance, no-condensate return system, no need for external mixers, no hammering and vibration, no scaling and fouling, and heating of liquids and slurries.
Want specifics? Here's how direct steam injection can help.
Water Heating. Heating water is a basic need for industry. Hot water is used in the production of food, pulp and paper, heavy metals, chemical and pharmaceuticals, grain milling and fermentation, water treatment and many others. Precise control of flow rate, output temperature and other factors are often critical to these processes. For example, in the food industry, a few degrees in water temperature can mean the difference between adequate sterilization and a food-safety issue.
In applications where non-water-miscible product is heated using a jacketed vessel (or kettle), direct steam injection's precise temperature control is a distinct advantage. Using water heated by direct steam injection in the jacket rather than steam provides better process control, eliminating the violent steam and water shock often associated with conventional jacketed kettle and reactor heating systems.
Pulp and Paper Stock Bleaching. Direct steam injection heaters can heat stocks and slurries at very high flow rates while precisely controlling temperature. This is needed in bleaching operations to minimize chemical usage, improve stock quality and reduce energy costs. Flow rates of up to 35,000 gal per min, producing a 2.8°F (1.6°C) temperature rise are common. Internally modulated heaters increase the maintenance interval, eliminate acid bath cleaning and, in some cases, eliminate the need for a mixer. Internal-modulation direct-steam injection heaters can effectively eliminate hammering and vibration.
Starch Cooking. For decades, a direct-steam injection heater has been used in the liquefaction stage of starch production. This requires near-instantaneous heating that fully cooks the starch evenly when operating under variable production rates. Internal modulation heaters provide a fully adjustable mechanical shear force to insure a complete cook-out of starch. With the proper turndown, smooth operation at varying slurry flow rates and temperature requirements can be assured. The self-cleaning feature on some internal modulation heaters eliminates cleaning-related downtime.
Specialty Direct Steam Injection Applications. Direct steam injection is versatile enough to heat heavy liquids with suspended solids as well as medium-to-thick slurries. The rule of thumb is, if it can be pumped, a direct steam injection heater can heat it. These heaters have been used to perform anaerobic digestion of wastewater slurries, in the extraction process for oil sands mining and processing other heavy slurries.
Applications for Direct-Contact Steam Injection
June 1, 2008