CHEE2020 Flashcards
(22 cards)
Design specifications?
- Equipment technology
- Equipment sizing and configuration
- Material of construction
- Control and safety features
- Sustainability features
Operating parameters
- Operating mode (batch, continuous)
- Process stream operating conditions (flow, temperature, pressure, composition)
- Equipment operating conditions (vessel pressure, liquid levels, equipment temp)
SIS trip system
takes action automatically to avert an unwanted event (eg shutting off pumping, closing valve…)
Interlock system
a group of devices that senses an off-limit condition or an improper sequence of events and acts to shutdown the process equipment.
Controlled variable guidelines
CV1. Not self-regulatory
CV2. Equipment/process constraints
CV3. Interactions with other loops (minimise)
Measured variable guidelines
MV1. Controlled variable
MV2. Easily measured
MV3. Sensitivity
MV4. Speed of response (minimise lag/ delay)
Manipulated variable guildelines
MPV1. Direct action
MPV2. Sensitivity (large gain)
MPV3. Speed of response (minimise lag/delay)
MPV4. Interactions with other loops (minimise)
Personal safety
may result in injuries to one or a few workers at a point in time
typically occur over a short timeframe and can occur frequently
falling on stairs
process safety
can result in severe damage to people, environment, assets, production,
an organisation’s reputation
are less common events that result from design flaws and/or a drift into
failure that occurs over longer timeframes
good personal safety
Taking responsibility for safe working
➢ Wearing necessary personal protective equipment
(PPE)
➢ Not working under influence of alcohol, drugs or
tiredness
➢ Being aware of hazards and risks
➢ Completing required workplace training
➢ Abiding by company procedure and rules
➢ Abiding by government regulations
Hazard
a source or a situation with the potential to cause harm to people, property, and
environment.
Hazards are generally associated with sources of energy e.g. chemical, thermal, kinetic,
potential energy
good process safety
Inherently safe design of plant
➢ Strong commitment to safety from senior
management
➢ Strong safety policies, procedures and
communication
➢ Well maintained equipment and plant
➢ Well trained staff
➢ Continuous learning about process safety
Risks
‘Risk is uncertainty that matters because it can positively or negatively affect the achievement of objectives
Risk is usually associated with uncertainty, unknown information, incomplete knowledge.
are the effects of the hazards
controlled variable
operating variable that needs to be controlled e.g. reactor
temperature, tank level, feed flowrate
set point
- target value for the controlled variable.
Measured variable
operating variable/s that is measured to determine how the unit/
equipment is performing e.g. reactor temperature, tank level, feed flowrate
Manipulated variable
operating variable that is changed to affect the controlled
variable e.g. tank outflow, steam flowrate
disturbance variable
operating variable that can disturb the process control loop
e.g. change in feed composition, feed flow, ambient conditions
Feedback control
➢ Compensates for disturbances after the
disturbance has affected the process
➢ Compensates for all disturbances (has no
intelligence on disturbance)
➢ Controlled and measured variables are the
same
➢ Very common in process industries
Feedforward control
➢ Compensates for a disturbance before it hits
the process
➢ Sensor is located on the fluctuating stream
➢ Relies on good understanding of the
dynamics of the process
➢ Uncommon to have straight FF in process
industries
Cascade control
➢ Two control loops working together –
master and slave loops.
➢ The output signal of the master loop
output acts as the setpoint for the
slave control loop.
➢ Slave loop typically adjusts for shortterm variations e.g. steam flow.
Master loop adjusts for longer-term
variations.
➢ May lead to better control for some
processes.
Ratio control
➢ Controls the proportion or ratio of two
variables
➢ Can be used to maintain two flows at a
constant ratio e.g. reagent flow/ process
feed flow to a reactor
