Equipment pt3

Chapter 11: Heat Exchangers

• Baffles are metal plates in tube bundles that hold tubes, provide support, and direct shell-side fluid flow.
• Double-pipe heat exchangers offer high reliability and handle high fouling potential.
• Water blasting is a surface cleaning technique using high-pressure water jets to remove deposits.
• Applying heat to an exchanger without a proper warm-up can rupture tubes due to thermal shock.
• Hydroblasting is a solution for fouling in heat exchangers.
• A condenser converts vapor to a liquid.
• Increased temperature difference between fluids raises the heat transfer rate.
• Conduction is the primary heat transfer mode used in heat exchangers.
• High-pressure leaks are often invisible but highly dangerous.
• Backwashing reverses flow to remove accumulated solids.
• Cross flow happens in heat exchangers with multiple passes and baffles.
• Turbulent flow is the ideal flow type for a heat exchanger.
• Parallel flow occurs when streams move in the same direction on both sides.
• Cold box heat exchangers are used in low-temperature processes.
• Finned tubing consists of thin plates increasing surface area for heat transfer.
• A tube sheet is a flat plate to which heat exchanger tubes are fixed.
• The removal of metal from chemical reactions within process fluid causes corrosion.
• Operating a heat exchanger with ruptured tubes may cause contamination.
• A preheater adds heat to fluids prior to a process operation.
• Rotary is NOT a type of heat exchanger.
• Establish the cold stream flow to the heat exchanger, as a step when starting up a shell-and-tube heat exchanger where the low-temperature fluid side is being filled.
• The shell is the outer covering of a heat exchanger retaining shell-side fluids.
• Low cost is an advantage of fixed tubesheet shell-and-tube heat exchangers.

Cooling Towers

• Heat Load (BTU/min) = Flow Rate (GPM) × 8.33 (weight of water in lb/gal) × ΔT (temperature difference in °F)
• Makeup Water (MU) = Drift Loss (DL) + Evaporative Loss (EL) + Blowdown Loss (BL)
• For 50,000 GPM, 100°F inlet, and 80°F outlet, the heat load in a cooling tower is 8,330 MBTUs/min.
• With 30,000 gpm water, 100°F inlet and 80°F outlet, where drift loss is 0.35%, evaporation is 1% per 10°F, and blowdown is 0.25%. The required makeup is 780 GPM.
• Cross-flow towers move water downward, while air goes horizontally.
• Water is 50-100 times more efficient at conducting heat than air.
• Drift eliminators minimize water loss.
• Failure to treat cooling water chemically can cause algae growth.
• Drift eliminators prevent water from being blown out.
• Circulating cooling water through a heat exchanger with ruptured tubes may cause process fluid contamination.
• Relative humidity represents the amount of water vs. the maximum air capacity.
• Humidity refers to the moisture content in the air.
• Wet and dry bulb temperatures are equal when humidity is 100%.
• Blowdown is the process for removing water and impurities.
• Natural draft cooling towers use temperature differences for air movement.
• Corrosion is the deterioration of metal by a chemical reaction.
• Tube leaks can result in process chemicals entering the circulating water.
• Closed-circuit cooling towers pass the working fluid through a heat exchange coil, and water is sprayed over it.
• Water distribution headers supply hot cooling water in forced and induced draft towers.
• Biocides are added at night when evaporation is lowest.
• Corrosion inhibitors prevent corrosion cooling tower piping and heat exchange equipment.
• Dissolved solids depositing in hot equipment results in scale.
• Grinding sounds are associated with pump cavitations.

Chapter 13: Furnaces

• A purge system removes combustible materials from the firebox.
• The draft control system regulates pressure in the combustion chamber.
• Process technicians adjust dampers and air registers and balance fuel to furnace flow rates.
• Induced draft uses a fan to draw flue gas from the furnace.
• Fans are used to purge combustibles from fireboxes in forced draft furnaces.
• It is important to wear a face shield when inspecting a natural draft furnace.
• NOx is a byproduct of fuel combustion at high temperatures, or when fuel contains nitrogen compounds.
• The bridgewall is located at or near the radiant section of a furnace.
• Examining uniform fire color and size should be included in a process technician's inspection.
• The bridgewall is a wall or vertical partition used to deflect heat.
• Insufficient air in a furnace leads to smoke, CO emissions, and explosions.
• The interlock control system shuts off the supply of fuel or process feed shutting down the furnace under certain conditions.
• Box furnaces heat process fluids or generate steam.
• Start-ups can create a high risk situation for spills and fires.
• Coking occurs when burner flames impinge on tubes.
• Natural draft has no mechanical draft or fans.
• Low speed on the draft fan can act as an interlock and shut down a furnace.
• Instrument malfunctions can cause improper fuel/air ratio, complete trip-out, and unnecessary shutdowns.
• Fuel type affects the time a tube can be in service before repair or replacement.

Chapter 14: Boilers

• Turn off the main shutoff valve during an emergency with a boiler.
• Spiders inject fuel into the boiler.
• Process technicians maintain boilers, while looking for flame impingement, wall hot spots and draft balance.
• Saturated steam is in equilibrium with water.
• Loss of boiler feedwater is a hazard that can cause tube rupture.
• Circulation of boiler water is based on convection.
• Start-up is the most hazardous operation in steam generation.
• Power outage can cause a loss of pumps and blowers.
• Mechanical trap is a common steam trap design.
• Huffing indicates improper draft operation.
• Knockout pots removes liquids/condensate from fuel.
• Draft fans supply combustion air to burners in water tube boilers.
• Deaeration removes gases from boiler feedwater by temperature increase via boiling.
• Downcomer tube is the cold-water line in a water tube boiler.
• Burners inject air and fuel to support combustion.
• Boiler feedwater pumps are prone to aging.
• Burners mix and burn fuel for heat.
• Filtration removes suspended matter in water softening systems.
• Shut off the steam is NOT a step in the typical start-up procedure for a boiler.
• Overheating can be caused by burner flame impingement or poor flame distribution.