Five free practice questions on steam in industrial plants: unit B12 of paper B (4B) of the 4th Class Power Engineer certificate exam, written to the SOPEEC syllabus. They are in the exam's format: four options, one correct answer. Answer each one before opening the explanation. No account, no email.
01The questions
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At a refinery, live steam is injected into the bottom of a side-stripper on the crude distillation column. What does the stripping steam do?
- Condenses in the oil and dilutes it before it is pumped away
- Heats the oil until its heavy fractions crack into lighter ones
- Lowers the hydrocarbon partial pressure so light ends boil off
- Blankets the column so air cannot get in and form a flammable mix
Show the answer
C. Correct. With steam in the vapour space the hydrocarbons supply only part of the total pressure, so light components still dissolved in the side-draw vaporize at a lower temperature and return to the column. That cleans up the product without heating it toward cracking; the steam leaves overhead and is condensed and separated.
Why not the others
A. Stripping steam leaves the top of the stripper with the vapours and is condensed overhead; it is not meant to stay in the product. Its job is lowering the hydrocarbon partial pressure.
B. Cracking needs much higher temperatures, or a catalyst, in units built for it. Stripping steam does the opposite job: it removes light ends without raising the temperature.
D. Steam purging clears air from equipment before start-up, but in a running column the stripping steam's job is to drive light ends out of the side-draw.
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A copper smelter's furnace off-gas leaves at well over 1 000 °C, laden with dust and sulphur dioxide, and must be cooled before the dust is removed and the sulphur dioxide is made into sulphuric acid. Which equipment cools the gas while recovering its heat?
- The converter of the downstream acid plant
- A water-spray quench tower in the gas stream
- An evaporative cooling tower in the plant yard
- A waste-heat boiler raising steam from the gas
Show the answer
D. Correct. Passing the off-gas through a waste-heat boiler cools it to a temperature the dust collectors and acid plant can take, and turns that heat into steam for power or process use. Without it, much of the furnace's heat would simply be thrown away.
Why not the others
A. The acid plant's converter is where the sulphur dioxide is oxidized; it takes cleaned, cooled gas and releases heat of its own. It cannot take raw, dusty furnace gas.
B. A water quench does cool the gas, but the heat goes into evaporating the spray water and is lost; it recovers nothing.
C. A cooling tower cools water by evaporation into air; it does not handle process gas. The gas itself must pass over heat-exchange surfaces to give up its heat usefully.
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At a heavy-oil lease, each vertical well goes through repeated cycles: steam is injected for several weeks, the well is shut in for some days, and then heated oil is produced from the same well for months until the next steam cycle. Which recovery process is this?
- In-situ combustion
- Steam-assisted gravity drainage
- Steam flooding between wells
- Cyclic steam stimulation
Show the answer
D. Correct. Cyclic steam stimulation uses one well for everything: inject steam to heat the reservoir, let it soak so the heat spreads and thins the oil, then produce from the same well until the rate falls and the cycle repeats. It is often called huff-and-puff.
Why not the others
A. In-situ combustion injects air and burns part of the oil underground to heat the rest; no steam is injected.
B. Steam-assisted gravity drainage uses a pair of horizontal wells, a steam injector a few metres above a producer, with injection and production running at the same time: heated bitumen drains down to the producer.
C. A steam flood injects continuously into injection wells and drives heated oil toward separate production wells; it does not inject and produce from the same well in turns.
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In a kraft pulp mill, the recovery boiler burns concentrated black liquor from the digesters. Besides raising steam, its purpose is to
- burn the bark and wood waste from the woodroom
- recover the cooking chemicals as a molten smelt
- dry the pulp sheet before it is cut and baled
- bleach the pulp by burning off the remaining lignin
Show the answer
B. Correct. Black liquor carries the spent cooking chemicals and the wood's dissolved lignin. Burning it releases the lignin's heat to raise steam, while the sodium and sulphur compounds collect on the furnace floor as molten smelt, which is dissolved and causticized to make fresh cooking liquor.
Why not the others
A. Bark and wood waste (hog fuel) are burned in a separate power boiler, often on a grate or in a fluidized bed. The recovery boiler burns black liquor to recover chemicals.
C. Pulp is dried on the pulp or paper machine over steam-heated dryer cylinders. The recovery boiler supplies some of that steam but does not dry the pulp itself.
D. Bleaching is a chemical process carried out in the bleach plant. The lignin in black liquor is burned as fuel, and the furnace's other product is the smelt of recovered chemicals.
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A cannery's steam retort is brought up to its process pressure of 103 kPa (gauge), with atmospheric pressure at 101.3 kPa; saturated steam at this pressure is at about 121 °C. The retort's pressure gauge and reference thermometer were both checked against calibrated instruments this week, yet the thermometer reads 113 °C. What is the most likely cause, and why does it matter?
- The cold cans are absorbing heat; the reading will catch up.
- The steam is superheated; cans will be over-processed.
- Air was not fully vented; cans may be under-processed.
- The steam is too wet; the cans will heat more slowly.
Show the answer
C. Correct. In a steam-air mixture the steam supplies only part of the total pressure the gauge reads, so the mixture is cooler than pure steam at that pressure, and air pockets also insulate the cans. The retort must be vented by its scheduled procedure until the temperature matches the pressure, or cans in cool zones may not reach the temperature needed to destroy spoilage organisms.
Why not the others
A. Cans do absorb heat while the retort comes up, but a space full of condensing steam at 204 kPa absolute is at 121 °C whatever the load. A low reading at full pressure means air remains.
B. Superheated steam would be hotter than 121 °C at this pressure, not cooler. A temperature below saturation at the gauge pressure means something other than steam is sharing the pressure: air.
D. Wet steam at a given pressure is still at its saturation temperature, 121 °C here; wetness means water droplets, not a lower temperature. The gap between pressure and temperature points to air.
02Answer key
| Question | Answer | Learning outcome |
|---|---|---|
| Q1 | C | Identify the Main Thermal Processes used in Oil Refining Industries |
| Q2 | D | Identify the Common Processes and Equipment used in Metallurgical Processing Plants |
| Q3 | D | Describe the main processes used in Steam Assisted Gravity Drainage (SAGD) and Cyclic Steam Stimulation (CSS) |
| Q4 | B | Identify the main Steam/Boiler Processes used in Wood and Biomass Processing Plants |
| Q5 | C | Identify the Important Thermal Processes used in Food Production and Preservation |
03What unit B12 covers
Where power engineers work and what the steam does there: thermal system pathways, heat-transfer-fluid heating, oil refining, SAGD and cyclic steam stimulation, gas separation and compression, wood and biomass processing, food production and preservation, and metallurgical processing.
Part B of the SOPEEC 4th Class syllabus names this unit “B12 Types of Plants” and lists one objective under it (objective 52 of 52). SOPEEC does not publish how many exam questions come from each unit, and neither do the ABSA, Technical Safety BC, TSASK or TSSA pages we checked. The right-hand column is how many questions our bank holds on each objective, Standard and Advanced together, not a count from the exam.
| Syllabus objective | In our bank |
|---|---|
| Objective 52 Identify steam-related processes in some common types of plants that employ Power Engineers. | 10 |
04What the questions turn on
Steam that does not come back
When a process injects steam directly into the product, none returns as condensate, so make-up water rises by the mass injected. In cyclic steam stimulation one well takes steam, soaks and then produces heated oil, cycle after cycle.
Steam as a stripping medium
Stripping steam in a refinery side-stripper lowers the hydrocarbon partial pressure so light ends boil off without heating the product toward cracking. In a sour-gas plant the regenerator's steam-heated reboiler boils the amine so its vapour strips out the acid gases.
Boilers that do a second job
A kraft mill's recovery boiler burns black liquor to raise steam and to recover the cooking chemicals as molten smelt. A smelter's waste-heat boiler cools the furnace off-gas for the dust collectors and acid plant while making steam from heat that would otherwise be lost.
Air spoils a steam process
Air left in a food retort makes a steam-air mixture that is cooler than pure steam at the gauge pressure, so cans may be under-processed until the retort is vented. A thermal-oil expansion tank is blanketed with nitrogen because hot oil in contact with air oxidizes and forms sludge.
05The other units
Paper 4B has twelve units, B1 to B12. Each has its own page of free questions:
The 4th Class Power Engineering practice exam (4B) page describes the full question bank; paper A has its own 4A practice exam. How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.