SUNAME AND INITIALS: MQENGQWA. A
STUDENT NO : 217289827
SEMESTER AND YEAR: YEAR
SUBJECT: THERMODYNAMICS II
ASSIGNMENT NUMBER : 1
LECTURER : Dr HASSAN
DUE DATE : 11 OCTOBER 2018
TABLE OF CONTENT
FLAME TUBE BOILER…………………………………………………….3
WATER TUBE BOILER…………………………………………………….4
WATER TREATMENT TECHNIQUES…………………………………..5
Boiler is a vessel, generally made of steel, in which is heated by some source of heat produced by combustion of fuel and ultimately to generate steam. The steam produced may be supplied at low pressure for industrial process work in Catton mills, sugar industries etc and for producing hot water which can be used to heating installations at much low pressure. Logically a steam boiler should have a minimum capacity of containing 10 litres of water and its minimum working pressure should be 3,4kgf/cm2.
Flame tube boiler
In a fire tube boiler, the flue gas travels through the tubes, which are surrounded by hot water. A flame tube boiler is a genre of boiler in which hot gases pass from fire through one or (many) more tubes running through a sealed container of water. The heat of the gases is transferred through the walls of the tubes by thermal conduction, heating the water and ultimately creating steam. Fire boilers are typically designed with either three or four set of tubes. Every set of tubes that the flue gas travels through is considered a “pass”. Looking at this scenario a boiler with more pass has a higher heat extraction rate and is more efficient than one with less pass. Fire tube boilers are not suitable for pressures above psing and actual operating steam output of fire tube boilers are less than the stated nameplate.
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Types of flame tube boiler
Scotch marine boiler:
The scotch marine boiler differs dramatically from its predecessor in using a large number of small-diameter tubes. The furnace remains a single large-diameter tube with the many small tubes arranged above it. They are connected together through a combustion chamber-an enclosed volume contained entirely within the boiler shell-so that the flow of fuel gas through the fire tubes is from back to front.
Locomotive-type boilers are used in traction engines, steam rollers, portable engines and some other steam road vehicle. The inherent strength of the boiler means it is used as the basis for the vehicle: all the other component, including the wheels, are mounted on brakes attached to the boiler. It is rare to find superheaters designed into this type of boiler, and they are generally much smaller (and simpler) than railway locomotive types.
Immersion fired boiler:
The immersion fired boiler is a single-pass fire-tube boiler that was developed.it has only fire tubes, functioning as a furnace and combustion chamber also, with multiple burner nozzles injecting premixed air and natural gas under pressure.
And many other types which are:
Vertical flame-tube boiler
Horizontal venture tubular boiler
Admiralty-type direct tube boiler
Water tube boiler
Water tube boilers are safer by design and generally can operate many years longer than fire tube boilers. A water tube boiler is such kind of boiler where the water is heated inside tubes and the hot gases surrounding them. Water boilers are available in longer larger capacities and recover faster than fire tube. Water tube boilers can also handle higher pressures, and have the ability to reach very high temperatures with the use of super heaters.
Application of flame tube boiler
flame tube boiler are best suited to low to medium steam generation and pressure applications where steam load is relatively constant and turn down and recovery are less critical such as commercial, institution and industrial heating, sainting and as steady state process boilers.
Working principle of water tube boiler
It consist of mainly two drums, one is upper drum called steam drum other is lower drum called mu drum. These upper drums and lower drum are connected with two tubes mainly down-comer and riser tubes as shown in the picture below.
Water in the lower drum and in the riser connected to it heated and steam is produced in them which comes to the upper drums naturally. In the upper drum, the steam is separated from water naturally and stored above the water surface. The colder water is fed from feed water inlet at the upper drum and as this water is heavier than the hotter water of lower drum and that in the riser, the colder water pushes the hotter water upwards through the riser. So there is one conventional flow of water in the boiler system.
Type of water tube boiler:
Horizontal straight water tube boilers:
Bent tube boiler:
Low head three drum
Advantages of water tube boiler:
Water tube boiler have additional advantage of small shell and tube diameters, so it occupies less space for a predefined steam capacity and pressure.
The larger heating surface can be achieved by using more numbers of water tubes.
Very high pressure in the order of 140 kg/cm2 can be obtained smoothly.
Water tube boilers due to presence of less water volume it will respond faster to load changes.
Thermal stress are reduced due to rapid circulation of coolant (water) in tubes due to convection.
The steam can be produced easily due to less volume of water on tube side and higher volumes of hot gases on shell side.
Disadvantages of water tube boiler:
Water tube boilers are very expensive in cost.
High quality feed water is required and little allowances for corrosion.
More complex control systems with very faster response times are required to control the water level in the steam drum due to the less volume of water in water tube boilers. In the event of loss water (coolant) the temperature in the water tube boilers rises quickly.
Application of water tube boiler:
The ability of water tube boilers to generate superheated steam makes these boilers particularly attractive in application that require dry meaning it is in gas state, high-pressure steam, including steam turbine power generation.
The use of water tube boilers is highly preferred in the following major areas:
Variety of process application in industries
Chemical process divisions
Pulp and paper manufacturing plants
Water treatment techniques used in boilers
Boiler water treatment is a type of industries water treatment focused on removal modification of substance potentially damaging to the boiler. And Impurities are removed
External treatment of raw water supplies intended for use within a boiler is focused on removal of impurities before they reach the boiler.
Internal treatment within the boiler is focused on limiting the tendency of water dissolve the boiler, and maintaining impurities in forms least likely to be cause trouble before they can be removed from the boiler blow down.
Internal treatment may be used above or in conjunction with external treatment. Its purpose is to properly react with feed water hardness, condition sludge, scavenge oxygen and prevent boiler water foaming. The water treatment facility purify and deaerate make-up water or feed water.
Treating boiler feed water is essentials for both high-and low-pressure boilers. Ensuring the correct treatment is implemented before problems such as fouling, scaling, corrosion occur, will go a long way in avoiding costly replacement/upgrades down the line.
An efficient and well-designed boiler feed water treatment system should be able to:
Efficiently treat boiler fee water and remove harmful impurities prior to entering the boiler
Promote internal boiler chemistry control
Maximize use of steam condensate
Control return-line corrosion
Avoid plant downtime and boiler failure
Prolong equipment service life.
Improving boiler efficiency:
Reduce excess air.
Blow down heat recovery:
Blow down of boilers to reduce the sludge and solid content allows heat to go down the drain.
Exhaust heat recovery:
This heat can be used to preheat boiler make-up water. Take care not to extract so much heat that the flue gases condense (causing corrosion).
Preheat combustion air
You may want to consider variable firing rates and/or dual fuel capabilities allowing you to choose the least expensive heating fuel at any given time. Natural gas burners can replace oil burners without requiring boiler replacement.
Tabulators and soot blow
Tabulator are metal baffles inserted into fire tube boilers to increase the heat transfer by increasing the surface area and slowing down the combustion gases. Soot blowers use steam or compressed air to help keep the fire-side surface of solid fuel or fired boilers clean.
Terry, K (2006) Boilers of steam, available at: http://www4.thermo.ac.uk/fas/eng/dcs/pdf (accessed: 08 0ctober 2013)
David, R (2006) engineering, available at: https://en.wikipedia.org>wiki>Boiler
Aves, F (2002) Boiler/engineering: https://www.britanica.com>technologyDavid, S (2004) Wall hung gas boilers-WIKA, available at: https://www.wika.co.za>industries_wall
Gorge, A (2001) Allmech products, available at: https:/www.allmech.co.za>boiler-division