This water-steam ratio is not sufficiently high to insure complete wetting of the tube walls in the outlet portion of the generator coil, therefore the maximum tube wall temperature must be determined using a steam rather than a water heat transfer film coefficient. The units are generally designed to produce approximately 80 per cent quality steam, so that the weight ratio of water to steam at the outlet of the generator is about 1:4, which is a much lower ratio than in conventional boiler designs. The once-through steam generator was specifically developed for thermal recovery applications and features a single pass of water through the generator coil and no separating drum. The high operating pressures used in this service dictate the use of a water tube design where the pressure is contained in relatively small tubes with resultant economy in manufacture and decrease in operating hazard. This paper is concerned only with reviewing the design concepts pertaining to the forced-circulation once-through generator. The production engineer is thus faced not only with the problem of understanding an unfamiliar piece of equipment, but evaluating the merits of several competitive designs. The result has been the appearance on the market of several competitive designs of thermal recovery generators. The generally satisfactory and sometimes spectacular results achieved in several of the initial commercial steam flooding projects has created a rapid increase in the requirement for suitable generators. The advent of high-pressure steam injection as a secondary recovery technique has created a requirement for a generator suitable for this application.

Steam alt gen