Fuel valves

With the advance of the turbine to idle speed, the turbine is ready to synchronize, and control is considered in synchronization. Both manual and automatic synchronizing are available locally. The unit is synchronized, and the main breaker closed. The speed reference will be switched to become a load reference. The speed/load reference will be automatically increased at a predetermined rate so that the fuel valve will be at the approximate position required for the desired load. For maintenance scheduling, the computer will count the number of normal starts and accumulate the number of hours at the various load levels. 

At Point 2, the air intake is closed, but compression does not begin until the exhaust port is covered also. Shortly after the exhaust port is closed and compression of the trapped air begins, fuel is injected at Point 3 into the cylinder through a high pressure fuel valve. At Point 4, just prior to completion of the compression stroke, a spark ignites the fucl/ iir mixture and the pressure rises rapidly through the remainder of the compression stroke and the beginning of the power stroke. 

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. 

Imperial Chemical Industries has introduced a new crystalline poly(ether ether ketone) (PEEK) (structure 4.78). Applications are for compressor plates, valve seats, thrust washers, bearing cages, and pump impellers. In the aerospace industry it is employed as aircraft fairing, fuel valves, and ducting. It is also used in the electrical industry as wire coating and semiconductor wafer carriers. 

In this particular example turbine speed control was taking place. The closed loop feedback is turbine speed in rpm as measured by an optical pickup on the generator box (nearly instantaneous). In this test, the experimental speed controller and the simulated speed controller (in both models), used a proportional gain of 0.001 and an integral gain of 0.001 x 0.75 with an input of speed error in rpm and output in fuel valve %. For the experiment presented, the fuel flow rate in grams per second... 

Bleed, cold bypass, hot bypass and fuel valve rh, x ... 

Step 2. This process has 14 control degrees of freedom. They include fresh feed valve DIB column steam, cooling water, reflux, distillate, and bottoms valves purge column steam, cooling water, reflux, distillate, and bottoms valves furnace fuel valve flooded condenser cooling water valve and DIB column feed valve. 

Step 2. There are 23 control degrees of freedom. They include two fresh feed valves for hydrogen and toluene purge valve separator base and overhead valves cooler cooling water valve liquid quench valve furnace fuel valve stabilizer column steam., bottoms, reflux, cooling water, and vapor product valves product column steam, bottoms, reflux, distillate, and cooling water valves and recycle column steam, bottoms, reflux, distillate, and cooling water valves. 

The detailed discussion of the burner design, operation, and control scheme is beyond this chapter and can be found in comprehensive published sources [8-11] as well as in multiple burner manufacturers brochures and technical publications. Most of the control system and fuel valve train requirements are specified (but not limited to) by the following codes ... 

Fuel valve closing time after N/A 5 sec maximum 1 sec maximum... 

Figure 10-1 shows a conventional single-loop control for a process heater. The loop usually contains a transmitter, a recorder-controller, and a fuel valve. 

Effect of Fuel Pressure. Another major problem with a conventioned single-loop control is that if the fuel pressure drops, less fuel will flow through the control valve. Eventually, the liquid flowing through the process heater will have a lower temperature which is finally affected by the thermocouple in the heater outlet. When this happens, the recorder-controller signals the fuel valve to open wider letting more fuel into the process heater. Unfortunately, more time passes before the controller knows precisely how much to open the fuel valve for correct temperature control. 

Effects of Process Flow Change. If the amount of process fluid to be heated suddenly decreases, some time will elapse before the thermocouple detects a temperature change and notifies the recorder-controller to reset the fuel valve. 

Effect of Valve Position. With some heating fluids, certain valve positions upset the supply of heat to the furnace which requires time for a change in process fluid temperature to be detected by the heater outlet thermocouple. When this happens, the controller will make an effort to reposition the fuel valve to satisfy the furnace heat... 

Effect of Other Conditions. During periods of heavy rain, combustion air temperature changes or a change in the amount of combustion air, and a change in the heater fuel temperature will have an effect on the process fluid outlet temperature. The result of these variables is that the controller is constantly trying to find a fuel valve position that will maintain a constant process fluid outlet temperature. 

The functions h), i) and j) are used when a two-shaft drive system needs to be simulated. When applied they usually require a special signal selection block to be incorporated just before the fuel valve or governor. The purpose of this signal selector is to automatically choose the lowest value or its two input signals, so that the least fuel is passed to the combustion system. This contributes to... 

A power amplifier to amplify the error signal and to provide sufficient power to supply the fuel valve actuator. 

The fuel valve actuator and its mechanism may have sufficient inductance or inertia to introduce a perceptible lag in the valve stem response to its input signal. The equivalent time constant is Tfi. 

Figure 2.18 Simulation of slewing of the fuel valve by using an exponential approximation.

If this approximation is made then an additional lag term should be inserted in the denominator of the fuel valve lag block described in sub section 2.6.1.7 and the hard limits simply applied to the output of the block. 

After the fuel valve moves from one position to another the flow rate of the fuel delivered to the combustors changes, but a delay due to the inertia of the fuel occms. The fuel enters the combustor and bums along its length at a finite burning rate. Completion of the combustion takes time and adds a further delay to the energy conversion process. A finite time is required for the burnt gas to pass through the power turbine and transfer part of its energy to the turbine. The turbine lead-lag block approximates these conversion processes. The number of lead and lag terms varies from one gas turbine type to another. 

The non-linear limits imposed on the control systems, e.g. constraints on excitation current, valve limits on fuel valves. 

Reverse power protection also protects a gas turbine from failure of its governor control system to regulate its speed e.g. component failure, sluggish response to speed changes. When power is fed back to the prime mover it will tend to cause the shaft speed to rise, and the governor control system will attempt to reduce the fuel supply by closing the fuel valve to its lower limit. In these circumstances the prime mover is effectively without speed control. 

Outflow of flue gas from tailpipe Intake of new charge of air and fuel Valves open... 

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