Secondary Refrigerant Research Articles

Crystallization of Ice in Direct Contact Crystallizer Agitated by the Buoyancy Force of Secondary Refrigerant

Crystallization of Ice in Direct Contact Crystallizer Agitated by the Buoyancy Force of Secondary Refrigerant

An integral design for desalination plant using the secondary refrigerant freeze process

A review of an earlier SRF design revealed the need for reappraisal, and has led to the identification of an integral design in which the four main process stages of the primary cycle are contained within separate compartments of a single vessel capable of producing up to 2 1 2 mgd (11,250 m 3/day). A commercial design using two integral vessels has been formulated and costed. Its capital cost is around 20% below the up-dated costs of the previous design and it shows the prospect of producing water at a level below those of competing systems.

Vapor-liquid equilibria of some pollutants in aqueous and saline solutions part II: correlation for dilute weak electrolytes in aqueous buffered solutions

A thermodynamic procedure is described for predicting vapor-liquid equilibria in buffered, dilute aqueous solutions containing one weak electrolyte: ammonia, hydrogen cyanide, formic acid, acetic acid, pyridine or aniline. The procedure requires the dissociation constant of the weak electrolyte and either the Henry's constant or a vapor-liquid equilibrium ratio ( K') determined for a dilute weak electrolyte solution in a pH region where most of the electrolyte is not ionized. Predicted results agree well with experiment. The thermodynamic procedure described here is effective for estimating phase equilibria for weak electrolyte pollutants in sea water or waste water as encountered in desalting plants or pollution abatement processes. The correlation is also useful in the design of secondary refrigerant freezing processes which utilize a direct contact melting-condensing system. In this scheme the volatiles present in the feed would be stripped out of solution by the evaporating refrigerant and then reintroduced to the product water.

Numerical determination of time responses of three flows heat exchanger in desalination plants

Three flows heat exchangers are essential components in vapour compression. vacuum freezing-vapour compression, secondary refrigerant freezing process desalination plants. In all these cases, the feed sea water flow is in counter current to the other two (fresh water product and waste brine). A numerical program is developed to determine the temperature time response of each of the three flows at any place along the heat exchanger for a step inlet temperature change of any one of the three flows. The case of random fluctuations of the inlet temperatures is also considered and solved by decomposing the inlet change of temperature versus time curve into a summation of steps of different magnitudes at equal time intervals, the overall response being the sum of all the responses to these steps.

Design features of secondary refrigerant freezing plants

The development of Secondary Refrigerant Freezing Plants (SRF) in the United Kingdom has reached a stage where the process has been adequately demonstrated on sizes up to 10,000 gpd (45m 3/day) and detailed estimates of commercial plant costs shown to be attractive. The paper outlines the approach to meet the stringent design requirements encountered on an actual site in the UK. and examines in detail the design considerations of the primary and secondary compressors. Additionally two other aspects, safety and environment, affecting component specifications are discussed.

The hydrolysis of halocarbon refrigerants in freeze desalination processes Part 1. Solubility and hydrolysis rates of Freon 114 (CClF 2CClF 2)

The solubility and rate of hydrolysis of Freon 114 (CClF 2 CCLF 2) have been measured over a range of conditions relating to secondary refrigerant freeze desalination technology. In this paper, results are presented for the solubility of gaseous Freon 114 between 0 and 50°C as a function of pressure in pure and saline water. The solubility of liquid Freon 114 has been calculated from vapor pressure data and Henry's law extrapolations. The magnitude of the calculated heat of solution is consistent with corresponding results for other fluorocarbon refrigerants. Semiempirical relations are also presented for solubility trends of fluorocarbon refrigerants as a function of molecular parameters of molar volume and polarizability. The very slow rates of hydrolysis of Freon 114 with and without catalysts have been followed with an ion selective membrane electrode which responds to fluoride ion activity. The significance of the results to the economics of refrigerant loss in freeze desalination plants is discussed. On the basis of the measured hydrolysis rates and estimated residence times based on feed flow for a typical plant, it is concluded that economic losses resulting from hydrolysis of Freon 114 would amount to less than 0.001¢ (U.S.) per 1000 gallons.

Vacuum stripping of butane from water in a packed column

When the freezing or hydrating of brine in a desalting process for producing fresh water is achieved by means of an extraneous refrigerating agent, whether it is an almost immiscible gas, such as butane, or a gas capable of forming hydrates, such as propane, CH 2ClF or other halogenated hydrocarbons, the outgoing products of brine and fresh water contain various amounts of the dissolved refrigerant. In the secondary refrigerant freezing process, the butane content in the product streams prior to degassing can vary between 80–140 ppm, depending upon the operating conditions. The hydrating agents are much more soluble, and the range is roughly from 0.1 to 3% by weight. The purpose of this study was to obtain data on the vacuum stripping of butane from water, and to analyze and interpret these data by means of current models of mass transfer, thus providing a sound basis for design. Butane was stripped from water down to concentrations as low as 0.6 ppm and the mass transfer rate was found to be liquid-diffusion controlled. The coefficients did not disagree with the predictive correlations of others, but a straightforward comparison was not possible. No particular design problems are foreseen in the stripping of butane down to very low concentrations, although additional data to predict heights of liquid transfer units at conditions of very high liquid to gas flow ratios would be useful.

The secondary refrigerant freezing process: A modeling study

The secondary refrigerant freezing process has been described by mathematical models of the major system components. The mathematical equations were used with the aid of a computer to study the operational-design economics of a freezing process and to predict the best operating conditions. Optimization computations showed that the economics of process operation depend largely on the temperature maintained in the freezer and the overall difference in refrigerant and equilibrium freezing temperature. The effect of departures from optimal design are assessed. An analysis of the linearized freezer dynamic equations showed the freezer to be stable and did not indicate regions of difficult control.

Nucleation and growth of ice crystals in secondary refrigerant freezing

A mathematical model of the freezing-crystallization step of the secondary refrigerant freezing desalination process has been proposed which takes into account the influence of the refrigerant phase on the nucleation rate. The moments of the crystal size distribution have been estimated assuming crystal growth occurs by either of two ways: by heat transfer limited growth, and by growth accompanied by agglomeration. Empirical constants for the nucleation rate and for agitator power efficiency were determined from data of several pilot plant tests. The agreement between observed and calculated size distribution moments indicated that the crystal growth model assuming agglomeration may be the more realistic.

Hydrate formation in i-butane- n-butane or a butene isomer water system at a given temperature

In this study- it was first confirmed experimentally that of the four-carbon hydrocarbons, only i-butane seems to be able to form solid hydrate by itself in coexistence with an aqueous phase. Then similar experiments with i-butanef-based binary mixtures with each of these hydrocarbons were carried out at a fixed temperature of -0.7°C. The results show that the relationships between the composition of the mixture used and the equilibrium total pressure can be found approximately by a proposed theoretical consideration. Thus, the mixtures with less than 73.8% i-butane can not form a hydrate at -0.7°C with 1.6% NaCl aqueous solution, and this limiting ratio increases with increasing temperature. For example, the following values are obtained: 84.1%, at 0.0°C and 69.5%, at -1.0°C. The mixtures containing more than the above ratios could form a solid hydrate, whose quantity was proportional to the excess of the i-butane used. Although to justify the above theory, it will be necessary to conduct further studies with propane instead of i-butane at this and/or at other temperatures, it suggests a suitable composition for the secondary refrigerant applied in the direct contact freezing process for the desalination of sea water, from the point of view of the operating pressure and the prevention of hydrate formation.

British Food Journal Volume 43 Issue 12 1941

British Food Journal Volume 43 Issue 12 1941