Chapter 1 Page 1 - 1.1 Define the following terms: setpoint, tim...

Chapter 1 Page 1

Chapter 1 Problem Solutions

1.1 Define the following terms: setpoint, time lag, a responsive variable, and a non- responsive variable. Setpoint: A setpoint is the standard value to which a measurement variable value is compared in order to assess how well a process is performing; it is the desired value of a variable.

 Time Lag: The delay between when a process stream is sampled for a

measurement variable and when a control variable makes an adjustment in response to the value of that variable. It is also often defined as the time between when a control variable makes an adjustment to the process and when the effect of the adjustment is evaluated by the controller (i.e. when the controller receives a measurement variable that is affected by the adjustment).

 Responsive Variable: A combination of process and measurement variable

dynamics such that the effect of a related control variable occurs and is measured

rapidly. Examples: pressure, temperature, and online (direct) analytical

measurements.

 Non-Responsive Variable: A combination of process and measurement variable

dynamics such that the effect of a related control variable occurs and/or is

measured slowly. Examples: level and indirect (sampled) analytical

measurements.

1.2 Explain the difference between a continuous process, a batch process, and a semi-batch process. Continuous Process: A process in which there is a constant flow of raw materials into and products out of the system (a steady-state process).

 Batch Process: A process that follows a sequence of different steps (process conditions) in order to transform raw materials into products. This type of system does not experience a steady flow of raw materials into and products out of the system, because of the delay which occurs from completing the steps required.

 Semi-Batch Process: This can be viewed as a batch process which is operated in a continuous way. By using several batch systems in parallel (often operating at different points in the sequence), a semi-batch process can take a constant flow of raw material and transform them into a steady flow of products.

1.3 Provide five examples of a semi-batch unit operation (hint: not an entire process, just a single unit operation). Filters: Often used when removing solids from either liquid or gaseous streams.These generally run between cycles of operation and cleaning.(Designing Controls for the Process Industries, 1e Wayne Seames) (Solution Manual, For Complete File, Download Link at the end of this File) 1 / 3

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 Fabric flue gas filters (shaker, backflow, etc.)  Mesh screens  Physical Adsorption Units: Most versions use a packed bed of sorbent to remove a chemical constituent from a gaseous or liquid stream. During use, the beds run until saturation and is then switched to a regeneration step. Pressure/Temperature Swing Adsorption  Molecular sieves

 Bio-reactors: Require an organism lifecycle in order to produce the

required/desired product concentrations. Photo Bio-Reactors for growing algae  Fermentation reactors for ethanol production  Drug synthesis reactors

 Blending/Mixing steps: Although blending and mixing steps are often run

continuously, there are some situations which require they operate as semi-batch.The most common reason for this is quality control testing required before the product can continue to packaging or additional processing. Paint blending tanks  Food manufacturing (mixing dough/batter/etc.)  These only represent some of the unit operations which are commonly run as a semi-batch

1.4 For each of the following measurement variables, classify the variable as “responsive” or “non-responsive”: temperature, level, pressure, direct in-process analysis, extracted process analysis, incompressible flow, and compressible flow.

 Temperature: Responsive

 Level: Non-Responsive

 Pressure: Responsive

 Direct in-process analysis: Responsive

 Extracted process analysis : Non-Responsive

 Incompressible flow: Responsive

 Compressible flow: Responsive

1.5 How do you keep a recycle loop from going out of control? In order to keep a recycle loop from going out of control, you need to dampen out the dynamic effects from the system to prevent them from being recycled. This is 2 / 3

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done by having a hold up spot. These hold-ups act as a dead space in the system where dynamic disturbances are allowed to dissipate before being recycled.

1.6 Gaseous butylene and isobutane react to form gaseous alkylate per the following reaction:

C4H8 + C4H10  C8H18 (1.1)

Feed streams are:

• Butylene feed containing 74 vol% butylenes, 17 vol% isobutene, 8 vol% n-

butane, and 1 vol% propane.

• Isobutane feed containing 90 vol% isobutane, 9 vol% n-butane, and 1 vol%

propane.

1.6.1 Draw an input/output diagram for a process that will produce 1700 m

3 /day of

alkylate. (hint: at mild conditions, mole% and volume% are essentially the same

for gases). See Drawing 1.6.1-A-001/1

1.6.2 If the reaction conversion is 25%, there is a substantial recycle stream in the

process. Assuming perfect separations allowing you to produce pure products:

propane, n-butane, and alkylate, draw a quantitative block flow diagram for the new unit. See Drawing 1.6.2-A-001/1

1.7 Using external resources such as the Internet or Process textbooks, find the information you need and draw an input/output diagram (without the material balance) for the

following processes:

1.7.1 The production of polyethylene from ethylene

 See Drawing 1.7.1-A-001/1

1.7.2 The separation of crude oil into: light gases, LPG, pentanes, naphtha, kerosene,

diesel, fuel oil, and tars  See Drawing 1.7.2-A-001/1

1.7.3 The conversion of methane into methanol

 See Drawing 1.7.3-A-001/1

1.7.4 The removal of CO2 from a power plant flue gas to generate a nearly pure CO2

waste stream

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