Steam metering

Serth, R.W. and W.A. Heenan, Gross Error Detection and Data Reconciliation in Steam-Metering Systems, AlChE Journal, 32(5), 1986, 7.3.3-742. 

Pressure-reducing stations, orifice plates, pitot tubes, and steam meters may all suffer from excessive mechanical wear and may therefore malfunction. 

For the flow of steam, a highly non-ideal gas, it is necessary to apply a correction to the calculated flowrate, the magnitude of which depends on whether the steam is saturated, wet or superheated. Correction charts are given by Lyle<5) who also quotes a useful approximation16 — that a steam meter registers 1 per cent low for every 2 per cent of liquid water in the steam, and 1 per cent high for every 8 per cent of superheat. 

Serth, R., and Heenan, W. (1986). Gross error detection and data reconciliation in steam metering systems. AIChE J. 32,733-742. 

Steam (or other) shaft power is furnished as a part of the rental privilege in some (5ases. In the case of steam the average power demand is estimated by taking indicator cards at the prime mover, with and without the power load in question. Steam as such may be sold by steam meter or (for heating) on the basis of the cubic feet or square feet of space rented. 

Reclaimer duty may be defined as pounds per hour of solution vaporized. This is equal to the steam flow to the reclaimer. If the steam meter isn t working, the operating engineer can measure the duty as follows ... 

A.m blent Environment. The environment around the flow conduit must be considered in meter selection. Such factors as the ambient temperature and humidity, the pipe shock and vibration levels, the avadabiHty of electric power, and the corrosive and explosive characteristics of the environment may all influence flow meter selection. Special factors such as possible accidental flooding, the need for hosedown or steam cleaning, and the possibiHty of lightning or power transients may also need to be evaluated. 

Vortex-shedding flow meters typically provide 1% of flow rate accuracy over wide ranges on Hquid, gas, and steam service. Sizes are available from 25 to 200 mm. The advantages of no moving parts and linear digital output have resulted in wide usage in the measurement of steam, water, and other low viscosity Hquids. 

Operating parameters of this German plant, on the basis of one cubic meter of raw gas, iaclude 0.139 m O2, 0.9 kg briquettes, 1.15 kg steam, 1.10 kg feed water, 0.016 kWh, and 1.30 kg gas Hquor produced. Gasifier output is 1850 m /h and gas yield is 1465 m /t dry, ash-free coal. The coal briquettes have a 19% moisture content, 7.8% ash content (dry basis), and ash melting poiat of 1270°C. Thermal efficiency of the gas production process is about 60%, limited by the quaHty and ash melting characteristics of the coal. Overall efficiency from raw coal to finished products is less than 50%. 

The highly exothermic nature of the butane-to-maleic anhydride reaction and the principal by-product reactions require substantial heat removal from the reactor. Thus the reaction is carried out in what is effectively a large multitubular heat exchanger which circulates a mixture of 53% potassium nitrate [7757-79-1/, KNO 40% sodium nitrite [7632-00-0], NaN02 and 7% sodium nitrate [7631-99-4], NaNO. Reaction tube diameters are kept at a minimum 25—30 mm in outside diameter to faciUtate heat removal. Reactor tube lengths are between 3 and 6 meters. The exothermic heat of reaction is removed from the salt mixture by the production of steam in an external salt cooler. Reactor temperatures are in the range of 390 to 430°C. Despite the rapid circulation of salt on the shell side of the reactor, catalyst temperatures can be 40 to 60°C higher than the salt temperature. The butane to maleic anhydride reaction typically reaches its maximum efficiency (maximum yield) at about 85% butane conversion. Reported molar yields are typically 50 to 60%. 

Meters. Diaphragms, diaphragm capsules, and bellows elements ate used extensively in meter bodies designed to measure differential pressure. These units can be used to measure the differences in pressure between two water lines, two steam headers, two stills, etc, from 25 Pa (0.1 in. H2O) to... 

International Steam Table) inch of water (39.2 F) newton/meter +02 2.490 82... 

An equation for use with venturi meters was given by Chisholm [Br Chem. Eng., 12, 454—457 (1967)]. A procedure for determining steam quahty via pressure-drop measurement with upflow through either venturi meters or sharp-edged orifice plates was given By Colhus and Gacesa [J. Basic Eng., 93, 11-21 (1971)]. 

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. 

FIG. 29-15 Approximate steam rate for single-stage turbines. To convert pounds per Idlowatthour to kilograms per Idlo-watthour, multiply by 0.4537 to convert inches to meters, multiply by 0.02 and to convert pounds per borsepower-bour to kilograms per Idlowattbour, multiply by 0.6084. 

FIG. 29-60 Excess head developed by lean and semilean pumps and the steam-throttle flow for a semdean-pump turbine. To convert gallons per minute to cubic meters per minute, multiply by 0.00379 to convert pounds per hour to kilograms per second, multiply by 1.260 X 10 . ... 

Fig. 1.2. A close-up of the mechanical lubricator on the traction engine. Unless the bore of the steam cylinder is kept oiled it will become worn and scored. The lubricator pumps small metered quantities of steam oil into the cylinder to stop this happening. The drive is token from the piston rod by the ratchet and pawl arrangement.

Metering flare gas is important for loss accounting and for control of steam injection. A special requirement for flare gas meters is low pressure drop and the ability to continue functioning in fouling conditions. The flare gas metering methods listed below have been used with varying degrees of success. 

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