Temperature, feed water operating pressure

Humidification. For wiater operation, or for special process requirements, humidification maybe required (see Simultaneous HEAT and mass transfer). Humidification can be effected by an air washer which employs direct water sprays (see Evaporation). Regulation is maintained by cycling the water sprays or by temperature control of the air or water. Where a large humidification capacity is required, an ejector which direcdy mixes air and water in a no22le may be employed. Steam may be used to power the no22le. Live low pressure steam can also be released directly into the air stream. Capillary-type humidifiers employ wetted porous media to provide extended air and water contact. Pan-type humidifiers are employed where the required capacity is small. A water filled pan is located on one side of the air duct. The water is heated electrically or by steam. The use of steam, however, necessitates additional boiler feed water treatment and may add odors to the air stream. Direct use of steam for humidification also requires careful attention to indoor air quahty. 

As the solubility of S02 in water is high, operation at atmospheric pressure should be satisfactory. The feed-water temperature will be taken as 20°C, a reasonable design value. 

Reverse-Osmosis Experiments. All reverse-osmosis experiments were performed with continuous-flow cells. Each membrane was subjected to an initial pure water pressure of 2068 kPag (300 psig) for 2 h pure water was used as feed to minimize the compaction effect. The specifications of all the membranes in terms of the solute transport parameter [(Dam/ 6)Naci]> the pure water permeability constant (A), the separation, and the product rate (PR) are given in Table I. These were determined by Kimura-Sourirajan analysis (7) of experimental reverse-osmosis data with sodium chloride solution at a feed concentration of 0.06 m unless otherwise stated. All other reverse-osmosis experiments were carried out at laboratory temperature (23-25 °C), an operating pressure of 1724 kPag (250 psig), a feed concentration of 100 ppm, and a feed flow rate >400 cmVmin. The fraction solute separation (/) is defined as follows ... 

Three pairs of membranes, each with two different porosities, were installed in the RO cells. The membranes used were PA (92 and 972), CAc (852 and 912), and PBI (892 and 992). Each cell had an effective membrane diameter of 4.1 cm (area of 13.4 cm2). The operating pressure for all runs was 260 10 psig, and the flow rate was adjusted to 410 10 mL/min. The system and membranes were washed by operating with an ethanol/water mixture (1 9 v/v twice) for a 6-8-h period to get rid of any trace organic impurities in the system. The system was then cleaned twice with purified water and equilibrated with purified water (3 X 10 h). During the run, the temperature of the feed solution increased from 20-22 °C to 26-29 °C. 

Pressure and temperature are the first operating conditions to be set. They are related the higher the pressure, the higher are the boiling temperatures of the feed and the products. In the case of high-pressure distillation it is economical to select the lowest operating pressure, which will permit satisfactory condensation of the distillate, and reflux at normal cooling-water temperatures [31]. 

The gaseous products of reaction, along with the supercritical water, leave the reactor. In some processes, effluent is used to preheat the feed to operating temperature, either by a heat exchanger, or by recirculating part of it towards the reactor. The remaining effluent is cooled and taken as emission at atmospheric pressure. 

Thus from a cold start at atmospheric pressure and without intervention by the operator distillation is in full swing in less than 45 minutes. The space heater is now in intermittent use, merely to float the still at the chosen operating temperature. Both load and capacity increase considerably with the temperature, so that the setting of the thermostat controls the output of the still. The constant electrical load of the still is now of the order of (1200 + 200 + 600) 100 ta 1500 100 watts. Factor rj is the proportion of time, less than unity, that the heater is energized and the factor 100 allows for the selected still temperature and the nature of the feed water, brackish or strongly saline. A breakdown of the energy requirements is shown in Table V. 

The boiler feed water deaerator reduced oxygen content to less than 7 ppb by the use of exhaust steam (low pressure). This system operated at lower temperature (110°C), used lower-pressure steam (0.05-MPa gauge), and achieved the oxygen specification without the use of chemical reducing agents as compared to conventional thermal desorption in a packed tower (7). 

Both catalyst activity and tar formation are directly affected by the state of hydration of the phosphoric acid-kieselguhr type of catalyst. At the higher temperature it is more difficult to maintain proper hydration. Hydration control is required because the catalyst has an optimum water content which determines the activity and selectivity of the catalyst. The water-vapor pressure varies at different catalyst temperatures and it is important to keep the water content of the hydrocarbon in equilibrium with that of the catalyst. In those units where water of saturation in the feed is insufficient, additional water must be injected into the feed as catalyst requirements dictate. The solid phosphoric acid type of catalyst contains the proper amount of water when manufactured and the art of catalyst hydration has reached such a point that catalyst in properly operated polymerization units no longer fails from coke formation or loss of activity. 

Figure 9.5 Operating pressure as a function of feed water temperature. Assumes 2000 ppm TDS at pH 7.6 feed water, 75% recovery, 3 2 1 array with 3 membranes per pressure vessel, FilmTec BW30-400/34 membranes.

As the H/C ratio in the feed decreases, the tendency to favor the production of carbon increases. Since the amount of water formed by combustion becomes insufficient, it is therefore necessary to operate in the presence of steam, even at elevated temperature. The thermodynamic calculation shows that, at identical temperatures, an increase in pressure results in larger water requirements and a decrease in oxygen requirements. Simultaneously, the residual methane content increases, and this can be offset by raising the temperature. The highest carbon content feedstocks (residues, coal, biomass) constitute the limit case.. ... 

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