Feedwater temperature

This efficiency can be improved by the use of a feed heating cycle whereby bled steam can be taken from the turbine after certain stages of expansion and then used to raise the feedwater temperature via use of feed heat exchangers. By such means the feedwater temperature. 

Although it would be possible to design for an economizer gas exit temperature of 30-50°C above the feedwater temperature, this would result in a temperature too close to the acid dewpoint of the gases. The acid dewpoint is the temperature at which acidic gases begin to condense out of the exhaust gas mixture. This is principally sulfuric acid due to the sulfur contained in the oil or coal. Although the bulk gas temperature may be satisfactory, in practice, the... 

A saving of (typically) 5 per cent can be made with gas-fired economizers, and as this is related to the boiler output it represents a saving of 6.25 per cent in fuel consumed. Gross heat-saving potential related to feedwater temperature and excess air level are shown in Figure 25.2. 

Given the system described in Example 10-11, what is (a) the combined heat and power efficiency assuming that cycle produces 2 tons/hr of 150 psia/400°F steam Assume a feedwater temperature of 60°F. 

Given 10,000 Ib/hr of 700°F cycle exhaust gas passing through a heat recovery boiler (HRB) (a) How much 150 psia, 400°F steam can be produced (b) How much heat is transferred from the gas to the steam (c) What is the exhaust temperature of the gas leaving the HRB and (d) Sketch the T-Q (temperature-heat) diagram for the HRB. Assume a gas side mean heat capacity of 0.25 Btu/lb, °F, an evaporator pinch temperature of 30°F, a feedwater temperature of 60°F, and an evaporator drum pressure of 180 psia to allow for pressure losses. 

The FT-30 membrane was found to be resistant to swelling or salt rejection losses at high feedwater temperatures. In simulated seawater tests, the membrane had stabilized at about 99 percent salt rejection at temperatures of 40°C and higher. 

The performance of a given membrane may be characterized according to its product flux and purity of product. Flux, which is a rate of flow per unit area of membrane, is a function of membrane thickness, chemical composition of feed, membrane porosity, time of operation, pressure across membrane, and feedwater temperature. Product purity, in turn, is a function of the rejection ability of the particular membrane. 

Specified that each of the four feedwater heaters accomplishes the same tei perature rise. Thus, the total temperature rise of 226 - 46 = ISO C is divided int four 45 C increments. This establishes all intermediate feedwater temperature at the values shown on Fig, 8.5. 

Because the pressure of this steam is kept constant, the feedwater temperature also stays constant, at the boiling point of water at the pressure of the LP steam, Ey... 

As a rule of thumb, the product water flow with constant net applied pressure will increase about 3% for each degree centigrade increase in feedwater temperature. Salt flux through the membrane is also directly proportional to temperature and the ratio of salt flux to water flux is essentially constant at different temperatures. This results in little or no change in rejection as a function of... 

Relative Potable Water Production Capability as a Function of RO System Feedwater Temperature... 

Decrease in Feedwater Temperature, Increase in Feedwater Flow, Increase in Steam Flow, and Inadvertent Opening of a Steam Generator Relief or Safety Valve... 

Such initiating events include loss of feedwater, excessive feedwater flow and reduction of feedwater temperature. 

A reduction of feedwater temperature due to failure of the heaters leads to an increase in steam flow through the fast acting steam dump valves to the de-aerators. However, cavitation can occur in the feedwater pumps, tripping them as a result of the pressure drop in the de-aerators. 

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