Steam flow rate

FIO. 29-37 Performance map showing the effect of pressure ratio and steam flow rate on a steam injection cycle. 

Determine Cj and C2 from Figure 2-31 and Table 2-11 for the steam flow rate and assumed pipe size respectively. Use Table 2-4 or Table 2-8 to select steam t eloc-ily for line size estimate. 

More usefully, since the steam flow rate is sought rather than the weight of steam. 

It is interesting to note that for a set steam flow rate and a given duty the steam pressure drop is higher when the liquid and steam are in countercurrent rather than... 

The pressure drop of condensing steam is therefore a function of steam flow rate, pressure and temperature difference. Since the steam pressure drop affects the saturation temperature of the steam, the mean temperature difference, in turn, becomes a function of steam pressure drop. This is particularly important when vacuum steam is being used, since small changes in steam pressure can give significant alterations in the temperature at which the steam condenses. 

As discussed, modelled and simulated by Prenosil (1976), the dynamics of the process bring in the question of steam consumption, steam flow rate, starting time of the distillation, and shut-down time when the desired degree of separation has been reached. The modelling of steam distillation often involves the following assumptions. 

The change in steam flow rate can be translated to changes in heating coil temperature. 

Saturated steam at 200psig (388°F, 2.13 ft3/lbm, /i = 0.015 cP) is fed from a header to a direct contact evaporator that operates at 10 psig. If the steam line is 2 in. sch. 40 pipe, 50 ft long, and includes four flanged elbows and one globe valve, what is the steam flow rate in lbm/hr ... 

The system shown in Figure El 1.4 may be modeled as linear constraints and combined with a linear objective function. The objective is to minimize the operating cost of the system by choice of steam flow rates and power generated or purchased, subject to the demands and restrictions on the system. The following objective function is the cost to operate the system per hour, namely, the sum of steam produced HPS, purchased power required PP, and excess power EP ... 

Boiler Steam flow rate, design pressure, steam superheat... 

Example 1.4. For the heat exchanger shown in Fig. 1.4, the load disturbances are oil feed flow rate F and oil inlet temperature Tq. The steam flow rate f, is the manipulated variable. The controlled variable is the oil exit temperature T. 

In most jacketed reactors or steam-heated reboilers the volume occupied by the steam is quite small compared to the volumetric flow rate of the steam vapor. Therefore the dymamic response of the jacket is usually very fast, and simple algebraic mass and energy balances can often be used. Steam flow rate is set equal to condensate flow rate, which is calculated by iteratively solving the heat-transfer relationship (Q = UA AT) and the valve flow equation for the pressure in the jacket and the condensate flow rate. 

PM = process measurement Tn = process inlet temperature r = process outlet temperature Fj = steam flow rate > = process flow rate... 

To illustrate the disturbance rejection effect, consider the distillation column reboiler shown in Fig. 8.2a. Suppose the steam supply pressure increases. The pressure drop over the control valve will be larger, so the steam flow rale will increase. With the single-loop temperature controller, no correction will be made until the higher steam flow rate increases the vapor boilup and the higher vapor rate begins to raise the temperature on tray 5. Thus the whole system is disturbed by a supply-steam pressure change. 

With the cascade control system, the steam flow controller will immediately see the increase in steam flow and will pinch back on the steam valve to return the steam flow rate to its setpoint. Thus the reboiler and the column are only slightly affected by the steam supply-pressure disturbance. 

Low-pressure steam flow rate to the intermediate reboiler is ratioed to feed rate, (e) Vapor sidestream flow rate is set by a temperature controlier holding tray 10 temperature. 

Base level is controlled by high-pressure steam flow rate to the base reboiler. 

A distillalion column is used to separate two close-boiling components that have a relative volatility close to one. The reflux ratio is quite high (IS) and many trays are required (150). To control the compositions of both products the flow rates of the product streams (distillate D and bottoms B) an manipulated. Gas chromatographs are used to measure the product compositions. Base level is controlled by steam flow rate to the icboiler and reflux drum level is controlled by reflux flow rate. 

Derive a dynamic mathematical model of the flooded-condenser system. Calculate the transfer function relating steam flow rate to condensate flow rate. Using a PI controller with tj = 0.1 minute, calculate the closedloop time constant of the steam flow control loop when a closedloop damping coefTident of 0.3 is used. Compare this with the result found in (u). 

The openloop transfer function relating steam flow rate to temperature in a feed preheater has been found to consist of a steadystate gain K, and a flrst-order lag with the time constant T. The lag associated with temperature measurement is t . A proportional-only temperature controller is used. 

A plant operator makes changes from time to time in various input variables such as feed flow rate, steam flow rate, and reflux flow rate from one operating level to a new level. These changes can be either instantaneous or gradual, as sketched in Fig. 14,7. These step-response data are often easily obtained by merely recording the variables of interest for a few hours or days of plant operation. 

Any type of input-forcing function can be used steps, pulses, or a sequence of positive and negative pulses. Figure 14.9a shows some typical input/output data from a process. The specific example is a heat exchanger in which the manipulated variable is steam flow rate and the output variable is the temperature of the process steam leaving the exchanger. 

A steam reheat Rankine cycle operates between the pressure limits of 5 and 1600 psia. Steam is superheated to 600° F before it is expanded to the reheat pressure of 500 psia. Steam is reheated to 600°F. The steam flow rate is 8001bm/hr. Determine the quality of steam at the exit of the turbine, the cycle efficiency, and the power produced by the cycle. 

Recovery factor calculations may not be possible under certain situations, including (1) a decrease in steam flow rate due to water breakthrough (2) scale deposits in the well-bore and/or fracture conduits (3) a fluctuating flow rate and (4) the completion of additional production wells in injection-affected areas, which will have an impact on the decline rates of nearby production wells. 

The same individual collecting the coal samples and maintaining the feed rates also recorded the air flow-steam flow rates in lbs/hr every 5 min. These values were used in conjunction with previously obtained flow data to approximate the stack gas flow rate during the test period. 

Figure 3.14. The lower ends of fractionators, (a) Kettle reboiler. The heat source may be on TC of either of the two locations shown or on flow control, or on difference of pressure between key locations in the tower. Because of the built-in weir, no LC is needed. Less head room is needed than with the thermosiphon reboiler, (b) Thermosiphon reboiler. Compared with the kettle, the heat transfer coefficient is greater, the shorter residence time may prevent overheating of thermally sensitive materials, surface fouling will be less, and the smaller holdup of hot liquid is a safety precaution, (c) Forced circulation reboiler. High rate of heat transfer and a short residence time which is desirable with thermally sensitive materials are achieved, (d) Rate of supply of heat transfer medium is controlled by the difference in pressure between two key locations in the tower, (e) With the control valve in the condensate line, the rate of heat transfer is controlled by the amount of unflooded heat transfer surface present at any time, (f) Withdrawal on TC ensures that the product has the correct boiling point and presumably the correct composition. The LC on the steam supply ensures that the specified heat input is being maintained, (g) Cascade control The set point of the FC on the steam supply is adjusted by the TC to ensure constant temperature in the column, (h) Steam flow rate is controlled to ensure specified composition of the PF effluent. The composition may be measured directly or indirectly by measurement of some physical property such as vapor pressure, (i) The three-way valve in the hot oil heating supply prevents buildup of excessive pressure in case the flow to the reboiier is throttled substantially, (j) The three-way valve of case (i) is replaced by a two-way valve and a differential pressure controller. This method is more expensive but avoids use of the possibly troublesome three-way valve.

This demonstration plant will normally operate at a first-effect boiling point of 250° F., a last-effect boiling point of 120° F., and a discharge sea water concentration factor of 4. The primary control of the process is accomplished by automatic control of steam flow rate, sea water flow rate, and last-effect vacuum. No control is needed for temperature or pressure in the individual effects and heat exchangers, since these achieve their own levels, influenced only by the proportioning of the equipment. The demonstration plant is rather heavily instrumented to permit close surveillance of operating conditions and carrying out of special tests. 

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