Ratio station

What we can do easily is to measure the fuel gas flow rate, multiply the value by R in the so-called ratio station, and send the signal as the set point to the air flow controller. The calculation can be based on actual flow rates rather than deviation variables. 

Up to this point, the ratio stations have all been outside the closed loops. But a natural extension to the configuration in Fig. 6.7 is the automatic repositioning of a master set point by the output of another controller. Consider the example of a chemical reactor which is to be operated consistently at maximum throughput, as determined by its heat-removal capability. The only control system which could satisfy this specification would feature a temperature controller setting the flow rates of all ingredients into the reactor, as shown in Fig. 6.8. 

FIG 6.7. A single master station can set all the plant streams through ratio stations. 

Most ratio stations have a gain range of about 10 1. Since the normal ratio setting for most applications is in the vicinity of 1.0, this is selected as the midscale position. (This assumes that the flowmeters for the various streams are sized in proper proportion, so that under normal operation they will all read about the same percentage flow.) Thus the gain of a typical ratio station would be adjustable from 0.3 to 3.0. 

The gain of the ratio station is the square of the ratio setting in other words, the ratio setting is the square root of the gain. The ratio scale for differential meters is compared with a linear scale below ... 

The total product flow is set into the controller manipulating stream, 4. The incoming concentration x is multiplied by the flow of the plant effluent F1, whih when added to stream Fj, gives a measure of total product in the blend. This same signal serves as the measurement for flow controller 1, and as a set point for flow controller 2. Blend concentration y is set into the ratio station at the right, manipulating the flow of solvent B. If the flow of the blend is F,... 

In Method II the flow rate of the disturbance stream is measured and transmitted to the ratio station (RS),... 

Regardless of how ratio control is implemented, the process variables must be scaled appropriately. For example, in Method II the gain setting for the ratio station Kfi must take into account the spans of the two flow transmitters. Thus, the correct gain for the ratio station is... 

Each transmitter output signal has a range of 4 to 20 mA. The transmitter spans are denoted by and for the disturbance and manipulated flow rates, respectively. Derive an expression for the gain of the ratio station Kr in terms of and the desired ratio R. ... 

Three demonstrations of the LIMB technology have been carried out. The first was a privately funded project in the 75 MWt Boiler 405 at the No. 4 AC Station of Inland Steel Industries, Inc. (56). By injecting 70 wt % minus 200 mesh (74 -lm) limestone, approximately 40% SO2 removal was achieved at a Ca S ratio of 3. This rose to 50% removal when the Ca S ratio was increased to 4. The second LIMB demonstration was the backup desulfurization system installed by B W as part of the relocation, repowering, and reconfiguration of the PCS power plant (46). 

The Bechtel confined zone dispersion (BCZ) process involves the injection of a fine slurry mist of pressure hydrated dolomitic lime or calcitic lime, using two-fluid atomizing nozzles. A demonstration at the 70 MWe Seward Station of the Pennsylvania Electric Co., performed in 15.2 m of ductwork with a 2.4-m by 3.4-m cross section, achieved a 50% removal of SO2 at a Ca S ratio around 1.1. 

Esi-ms measurements were performed on a Agilent LC M,SD system with the following operational parameters capillary voltage 4.0 kV, cone voltage, 50 V and solvent flow (methanol - water, 50% v/v) 0.3 inL/min. All esi mass specttal data in the positive ion mode were acquired and processed using HP Chem.Station software. The concenttation of aluminum was 0.5 mmol dm while that of mfx were varied in the interval 0.5-1.0 mmol dm. The pH values were pH 4.0, 6.0, 7.2 and 8.5. The specttum obtained at A1 to mfx concenttation ratio 1 2 and pH 4.0 is shown in Fig. 1. 

To have a modular construction with a wide choice of module sizes for optimum utilization of the usable area in each vertical panel, which is normally 1800 mm as illustrated in Figure 13,32, The general practice is to have the module sizes in the ratio of 1/6 (300 mm), 1/4 (450 mm), 1/3 (600 mm) and 1/2 (900 mm), etc. Some manufacturers, however, supply 1/8 (225 mm) and 1/9 (200 mm) size of modules when the sizes and number of components for a module are less and can be accommodated in such a small module size. For critical installations, however, such as for a refinery or a petrochemical plant or for the essential services of a powergenerating station or installations that are in humid conditions or are contaminated, it is advisable to have a module size no smaller than 1/6 (300 mm)... 

In electrical power stations a new measure of the performance is the amount of CO2 produced per unit of electricity generated, i.e. A = kg(C02)/kWh this quantity can be non-dimensionalised by writing A = A( 16/44)(LCV) where (16/44) is the mass ratio of fuel to CO2 for methane and (LCV) in its lower heating value. However, presenting the plant s green performance in terms of A directly allows the cost of any tax on the carbon dioxide to be added to the untaxed cost of electricity production most easily. 

At PicArsn (Ref 19), the fast neutron activation approach for detection of expls in suitcases was extended to the activation of both nitrogen and oxygen using two 7-ray detector stations in sequence. After 14 MeV neutron irradiation, the baggage is first monitored for 6.1 MeV 7-rays from the l60(n,p),6N reaction (7.5 sec half-life), followed by measurement of the 10 min 13N. Because expls are also rich in oxygen and have characteristic ratios of N/O, it was felt that this approach would increase the probability of detection with a corresponding decrease in the false alarm rate... 

Due to the imbalance of sources and sinks, atmospheric N2O is increasing by 3 Tg N/yr or 0.2%/yr. Figure 12-9 shows average N2O mixing ratios from four stations in the NOAA-CMDL network, Barrow, Mauna Loa, Samoa, and the South Pole (data are from the NOAA-CMDL and can be obtained from www.cmdl.noaa.gov). The most recent IPCC estimate gives a total N2O source of 16 Tg N, 7 Tg of which are a result of human activities (IPCC, 1997). The largest contribution to the anthropogenic N2O sources is 3 Tg N from... 

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