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Stationary Engineering Exam Questions and Answers
Typology: Exams
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What are drum internals? - Answer- Drums internals comprise all apparatus with in a drum, including all baffles that quiet or separate the steam and water, the various devices that may be used for affecting the separation of the steam and water, and the various chemical and feed water admissions piping and blow down lines What do scrubbers remove? - Answer- They remove the entrained moisture in the steam. The scrubber is not highly effective in removing small amounts of fine steam mist, but it suffices to eliminate most of the usual spray and splatter as well as to break up and eliminate any dry foam After passing through a washer, the moisture droplets in the steam are enlarged. This increases the effectiveness of the scrubber and helps reduce the carry-over. Explain how a scrubber works? - Answer- The steam passed between closely fitted corrugated plates or screens on which the mists are deposited in an action comparable to filtration. The velocity is low to avoid re-entrainment. The collected water is dripped by gravity to the boiler water below. The efficiency of the scrubber depends upon the following variables. a. Surface area b. Low steam velocity c. Steam passage irregularities d. Time of contact Name different types of water walls - Answer- Bare-Plate Walls- All internally fired, portable or integral fire box boilers, such as scotch marine or locomotive boilers. Bare-Tube Wall- They may be constructed of plain tubes, fin tubes or studded tubes, with a firebrick or refractory backing. Covered-Tubed Walls- Consist of tubes protected either by integral blocks or attached blocks. Blocks may be integral blocks of metal or attached blocks of metal, refractory or metal-enclosed refractory.
The purpose of the protection is to eliminate erosion and corrosion by the combustion products of waste heat, assist combustion, prevent escape of molten slag and provide a chill for a moving fuel bed What types of valves are found on a water wall header? - Answer- Blow-off connections are provided in each of the lower water wall headers for the removal of sludge. Care must be taken in making use of these blow downs. To avoid upsetting the circulation of water in the water wall, the water wall should never be blown down while the boiler is steaming. What is a forced circulation boiler? - Answer- Forced circulation is what makes controlled circulation possible. In the C & E design it involves the use of a pump or pumps to force water through all the steam-generating circuits. Thus insuring a positive flow in one direction at all times, regardless of the rate of heat application. Describe a box header - Answer- Two flat plates, the tube sheet and the handhole are flanged over. These are either joined together or joined to a wrapper sheet, by riveting. The flat surfaces are stayed by hollow steel stay bolts, screwed into each sheet and then riveted over against the sheet. The tubes are fastened to the tube sheet by being expanded in the tube holes and then are flared slightly to increase the holding power. What material is used to build a furnace wall? - Answer- Water tubes, firebrick, block- refractory face, cast iron, steel or ally steel. Insulating block, expanded metal, insulating cement, plastic and ceramic refractories. Insulation such as mineral wool and a steel exterior casing. What are the different types of brick used in boiler construction? - Answer- First-quality firebrick are made of fire clay having an alumina content of about 40% and fusion temperature of 3000 to 31000. Second and Third quality firebrick have lower alumina content and lower fusion temperatures and should ever be used in lining combustion chambers. Other refractory materials used in firebricks are kaolin, diaspore, cyanite and silicon carbide. What are steam risers and where are they located? - Answer- In water tube boilers the convection heating surface is arranged so that some of the tubes act as downcomers and the balance act as risers depending upon the relative amount of heat to which the tubes are exposed to direct radiant heat and higher temperatures, act as risers and the balance as downcomers. What is a riser tube? - Answer- a passage that routes water and steam into a drum from an upper water wall header.
What is the ramp rate of a boiler? - Answer- Ramp rate is the degrees Fahrenheit per hour rise that metal surface temperatures are exposed to when bringing up a boiler to rated conditions of temperature and load. Start up ramp rate is 3000 F/hour. What is a donkey boiler? - Answer- A donkey boiler is always an auxiliary boiler, such as one carried aboard a ship for use in port. What is a portable boiler? - Answer- An internally fired boiler intended primarily for temporary locations and obviously portable in construction and usage. Name types of soot blowers and their operation - Answer- Soot blowing fluid may be steam, (saturated or superheated) or compressed air. Soot blowers may be fixed or movable types, some are rotating and retractable and operated automatically and by remote control. The size, design and location of soot blower nozzles are varied to meet the cleaning needs encountered in the generation tube bank and other heat-exchanger equipment, including superheaters, air pre-heaters and economizers. It's important to keep the boiler steaming at a reasonably high rate while operating soot blowers. This avoids the possibility of flame out or the explosion of dead pockets filled unburned combustibles or fuel rich gas in some portions of the boiler. When blowing maintain a furnace draft of .10 to .15 inches of water Absorption rates of boiler parts (waterwalls, drum, SH, economizer etc) - Answer- BTU per hour per square foot Water walls - 50,000 - 80, Superheaters 8,000 - 12, Boiler 2,000 - 5, Economizer 3,000 - 4, Air Heater 500 - 700 Where are the baffles located on an "A" type boiler? - Answer- Between the 2 rows of tubes on the right and left hand sides. They are vertical and travel length of boiler, not width. What are arches? - Answer- Arches and baffle walls ensure thorough mixing and ignition of the air and combustible gases before they come in contact with the relatively cold metal of the boiler tubes.
Arches (among other functions) should be arranged to create turbulence, seal and protect the rear of the stoker, protect the grate , and assist ignition by direction particles of burning coal so they will fall on entering green coal. How are baffles supported and what are they made of? - Answer- Boiler baffles are made of refractory, alloy, or standard steel, depending upon the temperature of gases to which they are to be exposed. Refractory baffles are used near the furnace when high temperatures are encountered. They are constructed of special refractory shapes which are made to fit the exact location. Some baffles lie on a row of tubes and other run at an angle across the tubes. Where is the boiler blowoff taken from? - Answer- The bottom blowoff connection should be made to the lowest water-space practicable. (Blowoff connection should also be provided for each bottom waterwall header.) The piping should not be exposed to hot furnace gas unless protected. What is buttering? - Answer- It is when you use a dipper to pour fire clay batter over the brick. It is not good practice. Note: Each brick should be dipped into the fire clay mix and then pushed sideways into place so as to work the bond into irregularities in the face of the brick. When the brick is in place it should be tapped with a hammer to make sure the joint is as thin as possible. This way it is seldom necessary to use buttering. What are cyclone drum internals? - Answer- Purpose: eliminates carryover to improve steam quality. The cyclone separator overcomes many of the shortcomings for baffles and dry pipes. The operation of cyclone internals - Answer- a. steam and water from risers enter the drum from behind the baffle plate to mix with the water (washed) before entering the cyclone. The cyclone is open at top and bottom. b. water is thrown to the side of the cyclone by centrifugal force. c. additional separation of water and steam occurs in the passage of steam through the baffle plates. d. on entering the scrubber elements of water is also removed with steam passing to outlet header. Separators of this type can reduce the solids carry-over to a very low value depending on the type of feedwater treatment employed, the rate of evaporation and the water solids concentration. What is the purpose of drum internals? - Answer- Separation, washing and drying. In primary separation, the object is to separate a liquid from a vapor. This can be done by
utilizing gravity, change in direction of flow or impact against a plate. Centrifugal separators will handle foamy waters with more satisfactory results than ordinary baffles. What is steam washing? - Answer- Steam leaving a separator may contain small amounts of boiler water as steam borne spray or foam which contains boiler water concentrations of dissolved or suspended solids. Steam washing washes out, dilutes. or replaces this boiler water moisture and its high concentration of solids with fresh feedwater having relatively low salt concentration, so that a minimum of solid impurities will be left in the washed steam. Washing is a process of mixing rather than separating and must therefore be followed by a secondary stage of separation before the steam enters the dryer, or the latter may become overloaded. The proportion of available drum space required for the washing process is relatively great, and steam washing is feasible only in large diameter, single drum boilers, or inb boilers having more than one upper drum. An efficient steam washer functions as an open DE-aerating feedwater heater, and is often of value in minimizing corrosion through the elimination of excessive oxygen from boiler feed ( because of intimate contact of steam and wash water)