Heat treatment using steam

Heat as a sterilising agent is the method of choice for most effluent treatment plants, for a number of reasons  

The lethal effect of heat has been extensively and intensively studied for many years, and its kinetic characteristics well documented. No attempt is made here to discuss in detail principles of sterilisation or disinfection there is a large literature of standard text books to which the reader should refer. 

An empirical rule-of-thumb is often used in the design of sterilisation processes which uses the principle of substantial overkill to design a readily validated make-safe process. The MRC Working Party reports on pressure-steam sterilizers are often quoted as the intellectual source of the much-used sterilisation standard of saturated steam at 121.1 °C for 15 minutes. This treatment is widely regarded as giving a sufficient margin of safety in yielding a sterile product irrespective of the type and initial 

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The stabilisation of the zeolites using heat treatment under steam (vapour treatment) causes migration of aluminium out of the lattice. The result is the formation of an amorphous compound that can be detected by XRD in the form of a poorly defined scattering back-... 

More recently, surface heat treatments—using cooking, steam or hot water 26 -129a infra-red rays —have been developed for... 

Vacuum Treatment. Milk can be exposed to a vacuum to remove low boiling substances, eg, onions, garlic, and some silage, which may impart off-flavors to the milk, particularly the fat portion. A three-stage vacuum unit, known as a vacreator, produces pressures of 17, 51—68, and 88—95 kPa (127, 381—508, and 660—711 mm Hg). A continuous vacuum unit in the HTST system may consist of one or two chambers and be heated by Hve steam, with an equivalent release of water by evaporation, or flash steam to carry off the volatiles. If Hve steam is used, it must be cuUnary steam which is produced by heating potable water with an indirect heat exchanger. Dry saturated steam is desired for food processing operations. 

Water Treatment. Water and steam chemistry must be rigorously controlled to prevent deposition of impurities and corrosion of the steam cycle. Deposition on boiler tubing walls reduces heat transfer and can lead to overheating, creep, and eventual failure. Additionally, corrosion can develop under the deposits and lead to failure. If steam is used for chemical processes or as a heat-transfer medium for food and pharmaceutical preparation there are limitations on the additives that may be used. Steam purity requirements set the allowable impurity concentrations for the rest of most cycles. Once contaminants enter the steam, there is no practical way to remove them. Thus all purification must be carried out in the boiler or preboiler part of the cycle. The principal exception is in the case of nuclear steam generators, which require very pure water. These tend to provide steam that is considerably lower in most impurities than the turbine requires. A variety of water treatments are summarized in Table 5. Although the subtieties of water treatment in steam systems are beyond the scope of this article, uses of various additives maybe summarized as follows ... 

Tannins make excellent BW inhibitors. They are multifunctional, possessing several characteristics that make them entirely suitable for the treatment of HW heating and LP steam boilers. They also are generally suitable for use in industrial and process WT boilers at pressures of up to 650 or even 950 psig. 

Alternative proeesses for the reeyeling of fibre-reinforeed plastie (FRP), and their applieation in Japan, are briefly reviewed. Pulverised waste has been used in plastie mouldings for automotive applieations, and in eement roof tiles. FRP may be burned in ineinerators and used to heat water, or as an additive to eement kilns, where the resin aets as a fuel and the glass and filler beeome eement raw materials. Pyrolysis, in eonjunetion with metal eatalysts, has been used to reduee the waste to oils or gases, and treatment with steam or supereritieal water has also been sueeessfully applied. 26 refs. 

The oranges were washed, chopped in a meat mincer and homogenised by a Fryma mill. Water (0.6 volumes) were added before the slurry was heat treated by steam injection at 100°C for 2 minutes. The enzyme treatment was carried out for 1 hour at 40°C with 10 lU/g slurry of PME and 25 pg enzyme protein/g slurry of the other enzymes for each of the enzymes. The gelated orange slurry were treated at 85°C for 3 minutes to inactivate the enzymes before the strength of the gel was measured by a SMS TeJrture Analyser TA-XT2 (Stable Micro Systems, XT. RA Dimensions, Operations Manual versions) by compression analysis using a flat cylinder (20 mm dia.) with a speed of 2 mm/s. The force to provide a 20% compression was recorded. 

Commercial Masonite and Asplund boards and the asphalt-impregnated insulation board were sampled before any commercial heat treatment. The corresponding "thermomechanical" pulps had been produced by pressurized refining of steamed chips. The higher pre-steaming temperature used in the Masonite process resulted In a yield of about 85% as compared to a fiber yield of about 94% of the Asplund pulps, the remainder being dissolved. 

Requirements for vessels fabricated by forging in Part UF include unique design requirements with particular concern for stress risers, fabrication, heat treatment, repair of defects, and inspection. Vessels fabricated by brazing are covered in Part UB. Brazed vessels cannot be used in leth service, for unfired steam boilers, or for direct firing. Permitted brazing processes as well as testing of brazed joints for strength are covered. Fabrication and inspection rules are also included. 

UHT milk differs from pasteurized milk mainly in the heat treatment employed for sterilization. Usually UHT milk is heated at 130° to 150°C for 2 to 8 seconds and is then aseptically packaged. In the final heating stage, steam is injected directly into the milk, or the milk is infused into a steam chamber, followed by flash evaporation to remove added water (steam). An alternative procedure, the indirect method, involves heating milk across a stainless steel barrier, using high-pressure steam as the heating medium (Mehta 1980). 

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