Chapter 1: Introduction Flashcards
why do we need process control?
control makes it possible to operate the process by rejecting disturbances and keeping the process at its designed operating point. control keeps the process at steady state such that it is safe, efficient and profitable
what process constraints must be fulfilled
mass balance control and energy balance control
what producttion requirements must be fulfilled
production rate control and production quality control
if we’re measuring temperature then what are we trying to control?
temperature, what we’re trying to measure is what we’re trying to control
what do dotted lines represent
signals
what is the manipulated variable if we’re measuring the level
the manipulated variable if the flowrate of the outlet stream
what is the manipulated variable if we’re measuring the temperature?
the manipulated variable is the cooling water flowrate
what rules do we have for gas recycle loops
for gas recycle loops set at a maxiumum circulation rate to improve product yield and compressor operation
what rules do we have for liquid recycle loops
liquid recycle should have flow rate control to avoid snowball effect (variable flows of mass and energy round the recycle)
what rules do we have for material balance control structure?
control levels in the direction of flow ( use outflow as mv)
or
control levels in the reverse direction of flow ( use inflow as mv)
what does the flow controller do
the flow controller acts directly on the valve or pump to adjust the flowrate to the independent set point to ensure we meet production target
whats a throughput control
a throughput control measures flowrate through the process stream and is independently set. it is also known as production rate control
what is a sensor
a sensor is a measuring instrument and transmitter
LT, TT OR LI, TI
what are examples of an actuator?
valve, pump
what are examples of controllers
level controller, temperature controller, flow controller, pressure controller
LC,TC,FC,PC
how do we know what type of controller to use?
look at the set point and measurement
what relationship is there between level control and production rate control
there is an interaction between production rate control and level control
when the operator changes the set point for feed rate of A what happens to the feed rate of A
the flow of feed stream is at steady state until teh set point is changed.the flow rate then gradually increases but it needs time fort he system to respond to the system change and won’t immediately go to steady state. once it reaches the new set point value it eventually reaches steady state
what happen to level when the operator changes the set point for feed rate A
it goes to a maximum and then returns to level set point due to error signal from level controller
what happen to the product stream flow rate whenthe operator changes the set point for feed rate A
it will gradually increase until it reaches the new set point value. because there is no accumulation of mass Fin=Fout. so the new set point for the feed flow rate will also be the flowrate for the product stream.
what is a P&ID
piping and instrumentation diagram showing physical layout
what is a cause and effect diagram
shows cause and effect relationships, also called block diagram
what do the lines represent in a cause and effect diagram
the lines (wires) are not pipes. each wire represents a mathematical variable (also called a signal). the wires do not carry fluids
what does a temperature sesnor do in a cause an deffect diagram
the temperature sesnor measures the temperature of the reactor (physical quantity) and sends an electronic signal of the measurement of the reactor temperature