Makeup control

The controls are important, especially if low-percentage excess air is projected. Provide enough capital in the estimate to include metering type combustion controls, as mentioned earlier, and modern 3-element feedwater makeup controls. Stack oxygen monitoring should also be included. 

C. MAKEUP CONTROL. Another aspect of plant-wide control is the problem of "makeup control strategy. When a fresh feed stream is brought into a plant it... 

Figure 2.11 Ternary process with complete one-pass conversion of reactant B. (a) Ratio control structure with fixed reactant feed (unworkable) (i>) reactant makeup control based on component inventory ( workable).

Figure 2.13 Ternary process flowsheet with incomplete conversion and two recycle streams (.heavv-out-first sequence . iai Control structure CS4 reactor composition and level control (workable. (61 control structure CS1 reactant makeup control based on component inventories t workable).

When the setpoint of a dominant variable is used to establish plant production rate, the control strategy must ensure that the right amounts of fresh reactants are brought into the process. This is often accomplished through fresh reactant makeup control based upon liquid levels or gas pressures that reflect component inventories. Wre must keep these ideas in mind when we reach Steps 6 and 7. 

If we select temperature, we would like the reactor flow and composition to be nearly constant and we are constrained by the upper reactor temperature limit of 1300°F. If we select toluene composition, we can control it either directly or indirectly. If directly, a reactor feed composition analyzer is needed and is used to adjust either the fresh toluene feed rate or the total reactor toluene feed rate. If indirectly, the separation section is used as an analyzer for toluene. This allows us to control the total flow of toluene to the reactor (recycle plus fresh). Fresh toluene feed flow is used to control toluene inventory reflected in the recycle column overhead receiver level as an indication of the need for reactant makeup. Controlling the total toluene flow sets the reactor composition indirectly and is advantageous because it is less complicated and does not require an on-line analyzer. 

Low-level signals from the VCT initiate reactor makeup control or flow from the refueling water storage tank (RWST) as a backup. Makeup to the RCS can come from the sources listed below ... 

To borate the reactor coolant system, the operator sets the makeup control system to automatically add a preset amount of boric acid by fully diverting the three-way valve in the pump suction line to the boric acid storage tank, with delivered flow measured at the discharge of the makeup pumps. Dilution operates in a similar feshion. In either case, if the pressuriser level exceeds its control point, the letdown path to the liquid radioactive waste system holdup tanks is automatically opened by the protection and safety monitoring system. 

The primary water specifications for a PWR are given in Table 1 (4). Rigid controls are appHed to the primary water makeup to minimise contaminant ingress into the system. In addition, a bypass stream of reactor coolant is processed continuously through a purification system to maintain primary coolant chemistry specifications. This system provides for removal of impurities plus fission and activated products from the primary coolant by a combination of filtration (qv) and ion exchange (qv). The bypass stream also is used both to reduce the primary coolant boron as fuel consumption progresses, and to control the Li concentrations. 

Hydrating bentonite in fresh water before adding it to the mud greatly increases its efficiency when the makeup water is contaminated with salt and/or hardness. Prehydrated bentonite can be protected from dehydration by flgnosulfonate (70) or sulfomethylated tannin when used in saturated salt water. Salt water clays, such as sepioflte and attapulgite, provide no filtration control and are normally used with suitable filtration control agents. 

Decomposition by Caustic Scrubbing. The waste gas stream is led through packed towers where a sodium hydroxide solution is introduced at the top of the towers. Venturi scmbbers can also be used. Makeup sodium hydroxide is added under pH control (32). 

Tar sand feed contains a certain portion of fine minerals that, if allowed to build up in concentration in the middlings, increases viscosity and eventually dismpts settling ia the separation cell. The drag stream is required as a purge in order to control the fines concentration in the middlings. The amounts of water that can enter with the feed and leave with the separation cell tailings and froth are relatively fixed. Thus, the size of the drag stream determines the makeup water requirement for the separation cell. 

Boiler feed-water systems that use dernineralized or evaporated makeup or pure condensate may be protected from caustic attack through coordinated phosphate and pH control. Phosphate buffers the boiler water, reducing the chance of large pH changes due to the development of high caustic or acid concentrations. Excess caustic combines with disodium phosphate and forms trisodium phosphate. Sufficient disodium phosphate must be available to combine with all of the free caustic in order to form trisodium phosphate. 

In continuous dyeing there are many variables and the rapidity of the dyeing process requites many adjustments during the period in which several thousand meters of textile are dyed. Instmmental science has continued to advance rapidly so that continuous ranges are available which are entirely computer-controUed except for the makeup of the dye mix. These units feature computer control and closed-cincuit television and continuous color measurement techniques. 

A float valve is provided to control the supply of makeup water to replace the water vapor that has flashed off, Tne flash tank should be insulated. 

Important auxiliary equipment in a flotation plant includes feeder and controls, sampling and weighing devices, slurry pumps, filter and thickeners for dewatering solids, reagent storage and makeup equipment, and analytical devices for process control. 

The unit was built in a loop because the needed 85 standard m /hour gas exceeded the laboratory capabilities. In addition, by controlling the recycle loop-to-makeup ratio, various quantities of product could be fed for the experiments. The adiabatic reactor was a 1.8 m long, 7.5 cm diameter stainless steel pipe (3 sch. 40 pipe) with thermocouples at every 5 centimeter distance. After a SS was reached at the desired condition, the bypass valve around the preheater was suddenly closed, forcing all the gas through the preheater. This generated a step change increase in the feed temperature that started the runaway. The 20 thermocouples were displayed on an oscilloscope to see the transient changes. This was also recorded on a videotape to play back later for detailed observation. 

Tables 27-1 to 27-3 have concentrated on the personnel makeup of control agencies. For a broader look at places of employment. Table 27-4 shows where 8037 members of the Air Pollution Control Association (APCA) of the United States and Canada worked in 1982. (This list includes foreign as well as domestic members of APCA but does not include the membership of the air pollution control associations of other countries.) This table shows that only 10.7% of the members work in control agencies. This table gives a somewhat distorted picture because in many air pollution organizations only the senior executive, professional, and scientific personnel belong to APCA, whereas the total North American workforce in air pollution includes several times the 8037 membership total who are in junior, technical, service, or manual sectors and are not association members. These numbers could be still greater if those engaged in this work outside North America were included. The Air Pollution Control Association changed its name to the Air and Waste Management Association in 1988. The Air and Waste Management Association had a membership of over 14,000 in 1993, but only a portion of the members were active in the air pollution profession.

Mist eliminators are widely used in air polluhon control systems to prevent free moisture from entering the atmosphere. Usually, such mist eliminators are found downstream from wet scrubbers. The recovered mist is returned to the liquid system, resulhng in lowered liquid makeup requirements. 

Figure 30-lA presents the integrated environmental control potential for maximum control of particulate matter and SO2. Cooling tower water blowdown and treatment by-products may be used to satisfy scrubber makeup requirements. Fly ash and scrubber sludge will be produced separately. If the catalytic NO, process is required, the integration issues will be increased significantly. 

Fluidized-bed adsorbers have several disadvantages. The continuous handling and transport of solids is expensive from an equipment standpoint fluidized-bed systems must be large to be economical. Solids handling also presents a potential for mechanical problems. Careful control is required to keep the adsorbent fluidized, while minimizing adsorbent loss with the gas-phase attrition of the adsorbent can be high, requiring substantial makeup. 

Next, die mediod requires a determinatioa of die plant limits (i.e., die areas of the plant diat will be evaluated). Some hazards identified may be considered for on-site impacts. An experienced team of principal engineers, a HAZOP chairperson, and an external HAZOP e.xpert is die recommended makeup of the fouiidadon for die team. Other experts from other disciplines, such as instrumentation and process control, may be periodically called on to identify and evaluate deviations from normal operations. 

From the corrosion point of view, it is very important to control the deposition of scale. Removal of deposited scale by mechanical means is the first step. Standard, industrial water-treating techniques can be used to control scale deposition in general. In deep, hot wells or geothermal wells it is best to avoid untreated makeup water (i.e., geothermal brines). 

Salts are sometimes added to drilling muds to obtain certain desired mud characteristics. They can also enter the drilling fluid through contamination by addition of makeup water, formation-fluid inflow, and drilled formations such as salt domes, gypsum or anhydride formations. In freshwater systems, if salt contamination reaches undesirable levels, the following methods should be considered for control. 

The primary process variables affecting the economics of sulfuric acid alkylation are the reaction temperature, isobutane recycle rate, reactor space velocity, and spent acid strength. To control fresh acid makeup, spent acid could be monitored by continuously measuring its density, the flow rate, and its temperature. This can reduce the acid usage in alkyla-tion units. 

Plot properties of the fresh and equilibrium catalysts ensure that the catalyst vendor is meeting the agreed quality control specifications. Verify that the catalyst vendor has the latest data on feed properties, unit condition, and target products. Verify the fresh makeup rate. Check for recent temperature excursions in the regenerator or afterburning problems. 

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