Valve outlet temperature

We may calculate the valve outlet temperature, T 2, using the fact that the stagnation enthalpy will remain constant between the supply vessel and the valve outlet because the expansion is adiabatic (even though not reversible, and hence not isentropic) ... 

Rectifier pressure, kPa Distillate temperature, °K Condenser duty, W Stripper pressure, kPa Bottoms temperature, °K Reboiler duty, W Compressor duty, W Valve cooler duty, W Valve outlet temperature,"... 

At 192 min (3 h 12 min) the PORV block valve was reopened in an attempt to control reactor coolant pressure. Opening the valve resulted in an increase in the valve outlet temperature, a limited pressure spike in the reactor coolant drain tank (rupture disk had previously burst at 15 min), an increase in reactor building pressure, and a pathway by which hydrogen radionuclides from the damaged core could reach the reactor building. 

PORV and pressurizer safety valve outlet temperatures alarmed high. 

PORV outlet temperature was 285.4T. Safety valve outlet temperature was 270 F. 

Regenerative heat exchangers of both the fixed-bed and moving-bed types (67) have been considered for MHD use. The more recent efforts have focused on the fixed-bed type (68), which operates intermittently through recycling. A complete preheater subsystem for a plant requites several regenerators with switch-over valves to deflver a continuous supply of preheated air. The outlet temperature of the air then varies between a maximum and a minimum value during the preheat cycle. 

Schemes to control the outlet temperature of a process furnace by adjusting the fuel gas flow are shown in Figure 13. In the scheme without cascade control (Fig. 13a), if a disturbance has occurred in the fuel gas supply pressure, a disturbance occurs in the fuel gas flow rate, hence, in the energy transferred to the process fluid and eventually to the process fluid furnace outlet temperature. At that point, the outlet temperature controller senses the deviation from setpoint and adjusts the valve in the fuel gas line. In the meantime, other disturbances may have occurred in the fuel gas pressure, etc. In the cascade control strategy (Fig. 13b), when the fuel gas pressure is disturbed, it causes the fuel gas flow rate to be disturbed. The secondary controller, ie, the fuel gas flow controller, immediately senses the deviation and adjusts the valve in the fuel gas line to maintain the set fuel gas rate. If the fuel gas flow controller is well tuned, the furnace outlet temperature experiences only a small disturbance owing to a fuel gas supply pressure disturbance.

For partial condenser systems, the pressure can be controlled by manipulating vapor product or a noncondensible vent stream. This gives excellent pressure control. To have a constant top vapor product composition, the condenser outlet temperature also needs to be controlled. For a total condenser system, a butterfly valve in the column overhead vapor line to the condenser has been used. Varying the condenser cooling by various means such as manipulation of coolant flow is also common. 

The discharge temperature should be limited to 300°F as recommended by API 618. Higher temperatures cause problems with lubricant coking and valve deterioration. In nonlube service, the ring material is also a factor in setting the temperature limit. While 300°F doesn t seem all that hot, it should be remembered that this is an average outlet temperature, whereas the cylinder will have hot spots exceeding this temperature. 

In a simple single-loop system, we measure the outlet temperature, and the temperature controller (TC) sends its signal to the regulating valve. If there is fluctuation in the fuel gas flow rate, this simple system will not counter the disturbance until the controller senses that the temperature of the furnace has deviated from the set point (Ts). 

The proportional controller is reverse-acting so that the control valve throttles down to reduce steam flow as the hot water outlet temperature increases the control valve will open further to increase steam flow as the water temperature decreases. 

The basic reason for using different control-valve trims is to keep the stability of the control loop fairly constant over a wide range of flows. Linear-trim valves are used, for example, when the pressure drop over the control valve is fairly constant and a linear relationship exists between the controlled variable and the flow rate of the manipulated variable. Consider the flow of steam from a constant-pressure supply header. The steam flows into the shell side of a heat exchanger. A process liquid stream flows through the tube side and is heated by the steam. There is a linear relationship between the process outlet temperature and steam flow (with constant process flow rate and inlet temperature) since every pound of steam provides a certain amount of heat. 

For example, suppose we are controlling tbe process outlet temperature of a heat exchanger as sketched in Fig. 7.10. A control valve on the steam to the shell side of the heat exchanger is positioned by a temperature controller. To decide what action the controller should have we first look at the valve. Since this valve puts steam into the process, we would want it to fail shut. Therefore we choose an air-to-open (AO) control valve. 

What will the valve positions be if the total process flow is reduced to 25 percent of design and the process outlet temperature is held at 150" K ... 

Cooling water inlet and outlet temperatures are 80 and lOS F, respectively. The condenser heat transfer area is 1000 ft. The cooling water pressure drop through the condenser at design rate is 5 psi. A linear-trim control valve is installed in the cooling water line. The pressure drop over the valve is 30 psi at design with the valve half open. 

When overheated, hydrocarbons tend to breakdown, leaving carbon residues (coke). This coke builds up on the inside of the heater tubes, slowing the transfer of heat from the tube walls to the product by restricting the flow of product and acting as an insulator. As the control system attempts to maintain the process outlet temperature at the setpoint, the fuel valves will open and the tubes subjected to an increased heat load. With the diminished ability of this heat to be transferred to the process fluid, the temperature of the tubing will increase. 

The oldest, most direct method of pressure control is throttling on the cooling-water supply. This scheme is shown in Fig. 13.5. Closing the water valve to the tube side of the condenser increases the condenser outlet temperature. This makes the reflux drum hotter. The hotter liquid in the reflux drum creates a higher vapor pressure. The higher pressure in the reflux drum increases the pressure in the tower. The tower pressure is the pressure in the reflux drum, plus the pressure drop through the condenser. 

First, I tried opening valve A. Just as the chief operator said, the cooling-water outlet temperature increased, proving that water flow was reduced. Next, I checked the pressure at bleeder B it was 12 in Hg. The pressure was so low at this point because of... 

If we have the furnace on automatic temperature control while we are not using enough combustion air, and if the control valve on the fuel gas then opens to allow more fuel to the burners in order to either maintain or perhaps increase the furnace outlet temperature, the extra fuel will not burn efficiently. In fact, the extra fuel is likely to reduce the heater or furnace outlet temperature rather than increase or maintain it, as there is already a shortage of air and it cannot bum properly and tends to cool the firebox. The automatic temperature controller... 

Let s say we have a centrifugal refrigeration compressor, driven by a motor. The motor is tripping off because of high amperage. Should we open or close the suction throttle valve shown in Fig. 22.2 Answer— close it. Of course, both the evaporator vapor outlet temperature and the process fluid outlet temperature will increase. But that is the price we pay for having too small a motor driver on the compressor. Does this mean that when our home air conditioner gets low on freon, our electric bill drops Correct. But the price we pay is a hot home. 

When processes are subject only to slow and small perturbations, conventional feedback PID controllers usually are adequate with set points and instrument characteristics fine-tuned in the field. As an example, two modes of control of a heat exchange process are shown in Figure 3.8 where the objective is to maintain constant outlet temperature by exchanging process heat with a heat transfer medium. Part (a) has a feedback controller which goes into action when a deviation from the preset temperature occurs and attempts to restore the set point. Inevitably some oscillation of the outlet temperature will be generated that will persist for some time and may never die down if perturbations of the inlet condition occur often enough. In the operation of the feedforward control of part (b), the flow rate and temperature of the process input are continually signalled to a computer which then finds the flow rate of heat transfer medium required to maintain constant process outlet temperature and adjusts the flow control valve appropriately. Temperature oscillation amplitude and duration will be much less in this mode. 

Figure 3.9. Steam heaters, (a) Flow of steam is controlled off the PF outlet temperature, and condensate is removed with a steam trap or under liquid level control. Subject to difficulties when condensation pressure is below atmospheric, (b) Temperature control on the condensate removal has the effect of varying the amount of flooding of the heat transfer surface and hence the rate of condensation. Because the flow of condensate through the valve is relatively slow, this mode of control is sluggish compared with (a). However, the liquid valve is cheaper than the vapor one. (c) Bypass of process fluid around the exchanger. The condensing pressure is maintained above atmospheric so that the trap can discharge freely, (d) Cascade control. The steam pressure responds quickly to upsets in steam supply conditions. The more sluggish PF temperature is used to adjust the pressure so as to maintain the proper rate of heat transfer.

Nonetheless, there are running plants at laboratory and pilot-scale levels at institutes/universities and industry where process control is already exerted. Usually this is done in a rather conventional fashion, e.g. using commercial pressure hold valves and temperature determination at the in- and outlets and process-specific concentration monitoring outside the micro reactor. For example, an analysis of the redox potential was used for process monitoring for continuous azo pigment production at Clariant (see Figure 4.68) [99],... 

The control structure shown in Figure 6.57 is installed on the flowsheet. The feed is flow-controlled. The outlet temperature is controlled by manipulating the coolant flowrate. Note that the OP signal is sent to both of the control valves on the coolant stream, opening and closing them simultaneously. The setup works in the simulations, but it is not what would be used in a real physical system. A pressure-driven simulation in Aspen Plus requires that valves be placed on both the inlet and outlet coolant streams. In a real system, the cooling water would be drawn from a supply header, which operates a fixed pressure. A single control valve would be used, either on the inlet or on the outlet, to manipulate the flowrate of coolant. 

At 4 h, the feed composition is dropped to 2.5 mol% chlorine. Temperatures decrease sharply. The valve in the bypass line is driven completely shut at about 5.7 h, but the reactor inlet temperature cannot be maintained at the desired 400 K and drops to 393 K. The reactor outlet temperature drops from 500 to 438 K because of the reduction in reactant in the feed. Figure 7.32 shows the temperature profile at this new steady state. 

Where Q = Heat-Transfer Rate Fs = Steam Mass Flow AHs = Latent Heat of Vaporization F = Feed Rate Cp = Heat Capacity of Feed T0 = Steam Supply Temperature Pt = Steam Supply Pressure P2 = Steam Valve Outlet Pressure Ps = Condensing Pressure Tj = Inlet Temperature T2 = Outlet Temperature A Tm = Log Mean Temperature Difference Ts = Condensing Steam Temperature... 

CV Check Valve MV1 Manual Valve Inlet MV2 Manual Valve Outlet AV Automatic Valve Inlet Pressure Reaction Pressure Reaction Temperature Vessel Temperature Thermoswitch Safety Valve... 

FIGURE 11 Characteristic pilot plant vessel control strategy. Slave (secondary) controller based on jacket outlet temperature is shown. The control valve is on the outlet stream to minimize temperature gradients (when switching from hot to cold fluids) that would be imposed if the valve was on the inlet. (From ref. 18, with permission.)... 

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