Steam flow

Data Logger it acquires the external plant parameter signals (e.g. load steam flow, temperature and pressure etc.) required for correlation with the AE activity. 

Fig. 9. Schematic steam balance where the numbers represent steam flows in metric tons per hour. See Table 3.

Steam-Heated Exchangers Steam, the most common heating medium, transfers its latent heat in condensing, causing heat flow to be proportional to steam flow. Thus, a measurement olsteam flow is essentially a measure of heat transfer. Consider raising a hquid from temperature Ti to To by condensing steam ... 

Dynamically, the response of hquid temperature to a step in steam flow is that of a distributed lag, shown in Fig. 8-48. The time required to reach 63 percent complete response, X "t, is essentially the residence time of the fluid in the exchanger, which is its volume divided... 

Feedforward control can also be applied by multiplying the liquid flow measurement—after dynamic compensation—by the output of the temperature controller, the result used to set steam flow in cascade. Feedforward is capable of a reduction in integrated error as much as a hundredfold but requires the use of a steam-flow loop and dynamic compensator to approach this. 

A comparable statement can be made with regard to the power apphed to a mechanical recompression evaporator.) In summary, the steam flow required to increase the sohd content of the feed from Xq to X. is... 

FIG. 8 54 Controlling evaporators requires matching steam flow and evaporative load, here using feedforward control. 

From assumed feed temperature (forward feed) or feed flow (backward feed) to the first effect and assumed steam flow, calculate evaporation in the first effect. Repeat for each succeeding effect, checking intermediate assumptions as the calculation proceeds. Heat input from condensate flash can be incorporated easily since the condensate flow from the preceding effects will have already been determined. 

The result of the calculation will be a feed to or a product discharge from the last effect that may not agree with actual requirements. The calciilation must then be repeated with a new assumption of steam flow to the first effect. 

The two principal elements of evaporator control are evaporation rate a.ndproduct concentration. Evaporation rate in single- and multiple-effect evaporators is usually achieved by steam-flow control. Conventional-control instrumentation is used (see Sec. 22), with the added precaution that pressure drop across meter and control valve, which reduces temperature difference available for heat transfer, not be excessive when maximum capacity is desired. Capacity control of thermocompression evaporators depends on the type of compressor positive-displacement compressors can utilize speed control or variations in operating pressure level. Centrifugal machines normally utihze adjustable inlet-guide vanes. Steam jets may have an adjustable spindle in the high-pressure orifice or be arranged as multiple jets that can individually be cut out of the system. 

In a ouce-throiigh system, the feedwater entering the unit absorbs heat until it is completely couveided to steam. The total mass flow through the waterwall tubes equals the feedwater flow and, during uorm operation, the total steam flow As only steam leaves the boiler, there is no need for a steam drum. 

Cl Velocity of steam flow m/s ft/s Pmax Contact pressure, N/m ibftft ... 

The energy available in the steam is expressed in British thermal units per pound, or enthalpy. The velocity of the steam flow through the nozde is calculated from... 

The speed control operates the governing valve to maintain steam flow commensurate with load demand while holding speed essentially constant. For sudden load changes there will be a short-time overshoot, and a special case is the instantaneous loss of load, load dump at full load. The usual specification states that the overshoot on load dump must not exceed 9 to 10 percent of rated speed. The settled speed rise will of course be equal to the regulation, 4 or 6 percent for a NEMA Class C or B governor and less than I percent for Class D. 

The initial step in selection could logically be to make an estimate of the steam flow at various steam pressures by using Fig. 29-17 for a rough estimate of efficiency. Unfortunately, there are no rigid standards for steam pressure and temperature as electrical-voltage steps are fixed, and many engineers pick a pressure and a temperature... 

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

Measurement versus Expected Range If a steam flow is expec ted to vary in a relatively narrow range and the flow measure-... 

Steam turbine performance is modeled using a standard steam flow versus horsepower map and valve position versus steam flow. The turbine inlet valve(s) is positioned by the governor system to maintain constant speed (or another parameter when synchronized). 

A eurve of disk eooling steam flow versus expander inlet temperature shall be provided. 

O Steam Ejector Q Steam Press n Steam Flow ... 

Off-Design Performance—This is an important eonsideration for waste heat reeovery boilers. Gas turbine performanee is affeeted by load, ambient eonditions, and gas turbine health (fouling, ete.). This ean affeet the exhaust gas temperature and the air flow rate. Adequate eonsiderations must be given to bow steam flows (low pressure and high pressure) and superheat temperatures vary with ehanges in the gas turbine operation. 

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