Kaplan Turbine Working and Applications

⛲KAPLAN TURBINE ⛲

🌀The Kaplan turbine is a propeller-type water turbine which has adjustable blades. It was developed in 1913 by Austrian professor Viktor Kaplan who combined automatically adjusted propeller blades with automatically adjusted wicket gates to achieve efficiency over a wide range of flow and water level. The cost of kaplan turbine generally starts from ₹2.1 lakh rupees and it increases depending on our size and requirements 

🌀The Kaplan turbine was an evolution of the Francis turbine . Its invention allowed efficient power production in head applications which was not possible with Francis turbines. The head ranges from 10–70 metres and the output ranges from 5 to 200 MW. Runner diameters are between 2 and 11 metres. Turbines rotate at a constant rate, which varies from facility to facility. That rate ranges from as low as 54.5 rpm(Albeni Falls Dam)to 450 rpm.

🌀Kaplan turbines are now widely used throughout the world in high-flow, low-head power production.

⛲DEVELOPMENT OF THE K AS PLAN TURBINE ⛲

🌀Viktor Kaplan, living in Brünn, Austria-Hungary (now Brno, Czechia), obtained his first patent for an adjustable blade propeller turbine in 1912. But the development of a commercially successful machine would take another decade. Kaplan struggled with cavitation problems, and in 1922 abandoned his research for health reasons.

🌀In 1919 Kaplan installed a demonstration unit at Podebrady(now in Czechia). In 1922 Voith introduced an 1100 HP (about 800 kW) Kaplan turbine for use mainly on rivers. In 1924 an 8 MW unit went on line at lilla edet, Sweden. This launched the commercial success and widespread acceptance of Kaplan turbines.

⛲OPERATIONAL THEORY OF THE KAPLAN TURBINE ⛲

🌀The Kaplan turbine is an inward flow reaction turbine, which means that the working fluid changes pressure as it moves through the turbine and gives up its energy. Power is recovered from both the hydrostatic head and from the kinetic energy of the flowing water. The design combines features of radial and axial turbines.

🌀The inlet is a scroll-shaped tube that wraps around the turbine's wicket gate. Water is directed tangentially through the wicket gate and spirals on to a propeller shaped runner, causing it to spin.

🌀The outlet is a specially shaped draft tube that helps decelerate the water and recover kinetic energy. 

🌀The turbine does not need to be at the lowest point of water flow as long as the draft tube remains full of water. A higher turbine location, however, increases the suction that is imparted on the turbine blades by the draft tube. The resulting pressure drop may lead to cavitation. 

🌀Variable geometry of the wicket gate and turbine blades allow efficient operation for a range of flow conditions. Kaplan turbine efficiencies are typically over 90%, but may be lower in very low head applications.

🌀Current areas of research include computational fluid dynamics (CFD) driven efficiency improvements and new designs that raise survival rates of fish passing through.

🌀Because the propeller blades are rotated on high-pressure hydraulic oil bearings, a critical element of Kaplan design is to maintain a positive seal to prevent emission of oil into the waterway. Discharge of oil into rivers is not desirable because of the waste of resources and resulting ecological damage.

⛲VARIATIONS THAT CAN BE OBSERVED IN THE KAPLAN TURBINE ⛲

🌀The Kaplan turbine is the most widely used of the propeller-type turbines, but several other variations exist:

• Propeller turbines have non-adjustable propeller vanes. They are used where the range of flow / power is not large. Commercial products exist for producing several hundred watrs from only a few feet of head. Larger propeller turbines produce more than 100 MW. At the la grande-1 generating station in northern Quebec, 12 propeller turbines generate 1368 MW.

• Bulb or tubular turbines are designed into the water delivery tube. A large bulb is centered in the water pipe which holds the generator, wicket gate and runner. Tubular turbines are a fully axial design, whereas Kaplan turbines have a radial wicket gate.

• Pit turbines are bulb turbines with a gear box. This allows for a smaller generator and bulb.

• Straflo turbines are axial turbines with the generator outside of the water channel, connected to the periphery of the runner.

• S-turbines eliminate the need for a bulb housing by placing the generator outside of the water channel. This is accomplished with a jog in the water channel and a shaft connecting the runner and generator.

• The VLH turbine is an open flow, very low head "kaplan" turbine slanted at an angle to the water flow. It has a large diameter >3.55 m, is low speed using a directly connected shaft mounted permanent magnet alternator with electronic power regulation and is very fish friendly (<5% mortality).

• The DIVE-Turbine is a vertical propeller turbine with double regulation by wicket gates and speed variation. It covers a range of application up to 4 MW with efficiencies comparable to standard Kaplan-Turbines. Due to the propeller design with fixed blades it is considered a fish friendly turbine.

• Tyson turbines are a fixed propeller turbine designed to be immersed in a fast flowing river, either permanently anchored in the river bed, or attached to a boat or barge.

⛲APPLICATIONS OF KAPLAN TURBINE 

🌀Kaplan turbines are widely used throughout the world for electrical power production. They cover the lowest head hydro sites and are especially suited for high flow conditions.

🌀Inexpensive micro turbines on the Kaplan turbine model are manufactured for individual power production designed for 3 m of head which can work with as little as 0.3 m of head at a highly reduced performance provided sufficient water FLOW. 

🌀Large Kaplan turbines are individually designed for each site to operate at the highest possible efficiency, typically over 90%. They are very expensive to design, manufacture and install, but operate for decades.

🌀They have recently found a new home in offshore wave energy generation, see wave dragon. 

Pelton wheel turbine

⛲PELTON WHEEL TURBINE⛲

💧A Pelton wheel is an impulse-type water turbine invented by Lester Allan pelton  in the 1870s.The Pelton wheel extracts energy from the impulse of moving water, as opposed to water's dead weight like the traditional overshot water wheel. Many earlier variations of impulse turbines existed, but they were less efficient than Pelton's design. Water leaving those wheels typically still had high speed, carrying away much of the dynamic energy brought to the wheels. Pelton's paddle geometry was designed so that when the rim ran at half the speed of the water jet, the water left the wheel with very little speed; thus his design extracted almost all of the water's impulse energy—which allowed for a very efficient turbine.

⛲HISTORY ABOUT THE INVENTION OF PELTON WHEEL TURBINE ⛲

💧Lester Allan Pelton was born in Vermillion. Oheo in 1829. In 1850, he travelled overland to take part in the Califotnia gold rush.Pelton worked by selling fish he caught in the Sacrament river In 1860, he moved to Camptonville , a center of placer mining activity. At this time many mining operations were powered by steam engines which consumed vast amounts of wood as their fuel. Some water wheels were used in the larger rivers, but they were ineffective in the smaller streams that were found near the mines. Pelton worked on a design for a water wheel that would work with the relatively small flow found in these streams. 

💧By the mid 1870s, Pelton had developed a wooden prototype of his new wheel. In 1876, he approached the miners foundry in Nevada city,Califotnia to build the first commercial models in iron. The first Pelton Wheel was installed at the Mayflower Mine in Nevada City in 1878.The efficiency advantages of Pelton's invention were quickly recognized and his product was soon in high demand. He patented his invention on 26 October 1880. By the mid-1880s, the Miners Foundry could not meet the demand, and in 1888, Pelton sold the rights to his name and the patents to his invention to the Pelton Water Wheel Company in San Francisco. The company established a factory at 121/123 Main Street in San Francisco.

💧The Pelton Water Wheel Company manufactured a large number of Pelton Wheels in San Francisco which were shipped around the world. In 1892, the Company added a branch on the east coast at 143 Liberty Street in New York city.By 1900, over 11,000 turbines were in use. In 1914, the company moved manufacturing to new, larger premises at 612 Alabama Street in San Francisco. In 1956, the company was acquired by the Baldwin-lima-hamilton company , which ended manufacture of Pelton Wheels.

💧In New Zealand, A&G price in Thames. New Zealand produced Pelton waterwheels for the local market. One of these is on outdoor display at the Thames Goldmine EXPERIENCE.

⛲DESIGN INFORMATION OF THE PELTON WHEEL TURBINE ⛲

💧Nozzles direct forceful, high-speed streams of water against a series of spoon-shaped buckets, also known as impulse blades, which are mounted around the outer rim of a drive wheel (also called a runner). As the water jet hits the blades, the direction of water velocity is changed to follow the contours of the blades. The impulse energy of the water jet exerts torque on the bucket-and-wheel system, spinning the wheel; the water jet does a "u-turn" and exits at the outer sides of the bucket, decelerated to a low velocity. In the process, the water jet's momentum is transferred to the wheel and hence to a turbine. Thus, "impulse" energy does work on the turbine. Maximum power and efficiency are achieved when the velocity of the water jet is twice the velocity of the rotating buckets. A very small percentage of the water jet's original kinetic energy will remain in the water, which causes the bucket to be emptied at the same rate it is filled, and thereby allows the high-pressure input flow to continue uninterrupted and without waste of energy.

💧Typically two buckets are mounted side-by-side on the wheel, with the water jet split into two equal streams; this balances the side-load forces on the wheel and helps to ensure smooth, efficient transfer of momentum from the water jet to the turbine wheel.

💧Because water is nearly incompressible, almost all of the available energy is extracted in the first stage of the hydraulic turbine. Therefore, Pelton wheels have only one turbine stage, unlike gas turbines that operate with compressible fluid.

⛲WHAT ARE THE DESIGN RULES TO BE FOLLOWED WHILE DESIGNING A PELTON WHEEL TURBINE ⛲

💧The specific speed ${\displaystyle \eta _{s}}$  parameter is independent of a particular turbine's size.

💧Compared to other turbine designs, the relatively low specific speed of the Pelton wheel, implies that the geometry is inherently a "low gear" design. Thus it is most suitable to being fed by a hydro source with a low ratio of flow to pressure, (meaning relatively low flow and/or relatively high pressure).

💧The specific speed is the main criterion for matching a specific hydro-electric site with the optimal turbine type. It also allows a new turbine design to be scaled from an existing design of known performance.

${\displaystyle \eta _{s}=n{\sqrt {P}}/{\sqrt {\rho }}(gH)^{5/4}}$  (dimensioned parameter), 

where:

• ${\displaystyle n}$  = Frequency of rotation (rpm)
• ${\displaystyle P}$  = Power (W)
• ${\displaystyle H}$  = Water head (m)
• ${\displaystyle \rho }$  = Density (kg/m³)

💧The formula implies that the Pelton turbine is geared most suitably for applications with relatively high hydraulic head H, due to the 5/4 exponent being greater than unity, and given the characteristically low specific speed of the Pelton.

⛲PHYSICS INVOLVED IN PELTON WHEEL TURBINE ⛲

🌀Energy and initial jet velocity🌀

💧In the ideal (frictionless) case, all of the hydraulic potential energy (E_p = mgh) is converted into kinetic energy (E_k = mv²/2) (see bernoulli's principle). Equating these two equations and solving for the initial jet velocity (V_i) indicates that the theoretical (maximum) jet velocity is V_i = √2gh. For simplicity, assume that all of the velocity vectors are parallel to each other. Defining the velocity of the wheel runner as: (u), then as the jet approaches the runner, the initial jet velocity relative to the runner is: (V_i − u).The initial velocity of jet is V_i

🌀Final jet velocity🌀

💧Assuming that the jet velocity is higher than the runner velocity, if the water is not to become backed-up in runner, then due to conservation of mass, the mass entering the runner must equal the mass leaving the runner. The fluid is assumed to be incompressible (an accurate assumption for most liquids). Also it is assumed that the cross-sectional area of the jet is constant. The jet speed remains constant relative to the runner. So as the jet recedes from the runner, the jet velocity relative to the runner is: −(V_i − u) = −V_i + u. In the standard reference frame (relative to the earth), the final velocity is then: V_f = (−V_i + u) + u = −V_i + 2u.

🌀Optimal wheel speed🌀

💧We know that the ideal runner speed will cause all of the kinetic energy in the jet to be transferred to the wheel. In this case the final jet velocity must be zero. If we let −V_i + 2u = 0, then the optimal runner speed will be u = V_i /2, or half the initial jet velocity.

🌀Torque🌀

💧By newton's second and third laws of motion, the force F imposed by the jet on the runner is equal but opposite to the rate of momentum change of the fluid, so

F = −m(V_f − V_i)/t = −ρQ[(−V_i + 2u) − V_i] = −ρQ(−2V_i + 2u) = 2ρQ(V_i − u),

where ρ is the density, and Q is the volume rate of flow of fluid. If D is the wheel diameter, the torque on the runner is

T = F(D/2) = ρQD(V_i − u).

💧The torque is maximal when the runner is stopped (i.e. when u = 0, T = ρQDV_i). When the speed of the runner is equal to the initial jet velocity, the torque is zero (i.e. when u = V_i, then T = 0). On a plot of torque versus runner speed, the torque curve is straight between these two points: (0, pQDV_i) and (V_i, 0).Nozzle efficiency is the ratio of the jet power to the water power at the base of nozzle

🌀Power🌀

💧The power P = Fu = Tω, where ω is the angular velocity of the wheel. Substituting for F, we have P = 2ρQ(V_i − u)u. To find the runner speed at maximum power, take the derivative of P with respect to u and set it equal to zero, [dP/du = 2ρQ(V_i − 2u)]. Maximum power occurs when u = V_i /2. P_max = ρQV_i²/2. Substituting the initial jet power V_i = √2gh, this simplifies to P_max = ρghQ. This quantity exactly equals the kinetic power of the jet, so in this ideal case, the efficiency is 100%, since all the energy in the jet is converted to shaft output.

🌀Efficiency🌀

💧A wheel power divided by the initial jet power, is the turbine efficiency, η = 4u(V_i − u)/V_i². It is zero for u = 0 and for u = V_i. As the equations indicate, when a real Pelton wheel is working close to maximum efficiency, the fluid flows off the wheel with very little residual velocity.In theory, the energy efficiency varies only with the efficiency of the nozzle and wheel, and does not vary with hydraulic head.The term "efficiency" can refer to: Hydraulic, Mechanical, Volumetric, Wheel, or overall efficiency.

⛲SYSTEM WORKING OF THE PELTON WHEEL TURBINE⛲

💧The conduit bringing high-pressure water to the impulse wheel is called the penstock. Originally the penstock was the name of the valve, but the term has been extended to include all of the fluid supply hydraulics. Penstock is now used as a general term for a water passage and control that is under pressure, whether it supplies an impulse turbine or not.

⛲APPLICATIONS OF PELTON WHEEL TURBINE⛲ 

💧Pelton wheels are the preferred turbine for hydro-power where the available water source has relatively high hydraulic head at low flow rates. Pelton wheels are made in all sizes. There exist multi-ton Pelton wheels mounted on vertical oil pad bearnings in hydroelectric plants. The largest units – THE Bieudron hydroelectric power station at the grande dixence dam complex in Switzerland – are over 400MW(MEGAWATTS). 

💧The smallest Pelton wheels are only a few inches across, and can be used to tap power from mountain streams having flows of a few gallons per minute. Some of these systems use household plumbing fixtures for water delivery. These small units are recommended for use with 30 metres (100 ft) or more of head, in order to generate significant power levels. Depending on water flow and design, Pelton wheels operate best with heads from 15–1,800 metres (50–5,910 ft), although there is no theoretical limit.

⛲ACCORDING TO THE ARTCILE BY"INTERNET SHOTS"⛲

🌀Global Pelton Hydro Turbine Runner Market Forecast by Type and by Application (2021-2026) with Detailed Development History🌀

💧A pelton wheel has one or more free jets discharging water into an aerated space and impinging on the buckets of a runner. Draft tubes are not required for impulse turbine since the runner must be located above the maximum tailwater to permit operation at atmospheric pressure.

💧The global Pelton Hydro Turbine Runner market is valued at US$ xx million in 2019 is expected to reach US$ xx million by the end of 2026, growing at a CAGR of xx% during 2020-2026.Global Pelton Hydro Turbine Runner Market: Drivers and Restrains:

💧The research report has incorporated the analysis of different factors that augment the market’s growth. It constitutes trends, restraints, and drivers that transform the market in either a positive or negative manner. This section also provides the scope of different segments and applications that can potentially influence the market in the future. The detailed information is based on current trends and historic milestones. This section also provides an analysis of the volume of production about the global market and also about each type from 2015 to 2026. This section mentions the volume of production by region from 2015 to 2026. Pricing analysis is included in the report according to each type from the year 2015 to 2026, manufacturer from 2015 to 2020, region from 2015 to 2020, and global price from 2015 to 2026.

💧A thorough evaluation of the restrains included in the report portrays the contrast to drivers and gives room for strategic planning. Factors that overshadow the market growth are pivotal as they can be understood to devise different bends for getting hold of the lucrative opportunities that are present in the ever-growing market. Additionally, insights into market expert’s opinions have been taken to understand the market better.

💧The major players in the market include Andritz, Voith, GE, Toshiba, Dongfang Electric, BHEL, Hitachi Mitsubishi, Harbin Electric, IMPSA, Zhefu, Power Machines, CME, Marvel, Global Hydro Energy, Zhejiang Jinlun Electromechanic, Tianfa, Litostroj Power Group, Gilkes, GUGLER Water Turbines, Geppert Hydropower, FLOVEL, DE PRETTO INDUSTRIE SRL, Franco Tosi Meccanica, etc.

boilers and classification of boilers

🔎What is a boiler? 

🔥A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central heating, boiler-based power generation, cooking, and sanitation.

🔥CLASSIFICATION OF BOILERS🔥

♨️Boilers are classified in many different ways. some important methods are discussed below.

♨️ Boilers are commonly classified as fire tube or water tube boiler based on the way the water and gases pass through them.

Based on the type of fuel used, boilers are classified as coal-fired, oil fired or gas-fired boilers.

♨️Boilers are also classified based on their method of manufacture such as packaged boilers or field-erected boilers.

Based on end application, boilers are classified as utility, industrial, or marine boilers.

♨️A further of classification includes pressure level(low pressure, subcritical pressure, supercritical pressure, etc.) and the type of circulation(natural, pumped, once through, combined).

1️⃣ FIRE TUBE BOILER

♨️A typical externally fired, fire-tube boiler schematic as shown in figure.

The main advantages of fire-tube boilers are that they are simpler in design and generally lower in initial cost compared to water of equal capacity.

♨️They require less draught.

♨️Limitations of fire-tube boilers are limited pressure and capacity. So it is not used in a power sector.

♨️Compared to water-tube boilers, they are slower to respond to demand for steam. Also, stresses are greater in boilers because of their rigid design and subsequent inability to expand and contract easily.

TYPES OF FIRE TUBE BOILER 

♨️According to the location of furnace there are two types of fire tube boiler and these are external furnace and internal furnace type.
♨️There are mainly three types of external furnace fire tube boiler.

1. Horizontal return tubular fire tube boiler.
2. Short fire box fire tube boiler.
3. Compact fire tube boiler.

♨️There are also two types of internal furnace fire tube boiler

1. Horizontal tubular.
2. Vertical tubular fire tube boiler.

🔥WORKING OF HORIZONTAL RETURN FIRE TUBE BOILER🔥

♨️Horizontal return fire tube boiler is most suitable for low capacity thermal power plant . The main constructional features of this boiler are one big size steam drum which lies horizontally upon supporting structures. There are numbers of fire tubes come from furnace and also aligned horizontally inside the drum. When the drum is filled with water these tubes are submerged in water.

♨️The fuels (normally coal) burnt in the furnace and combustible gasses move into the fire tubes, travel through these tubes from rear to front of the boiler drum and finally the gases come into the smoke box. The hot gasses in the tubes under water transfer heat to the water via the tube walls. Due to this heat energy steam bubbles are created and come upon the water surface. As the amount of steam is increased in that closed drum, steam pressure inside the drum increases which increase significantly the boiling temperature of the water and hence rate of production of steam is reduced. In this way a fire tube boiler controls its own pressure. In other words this is a self pressure controlled boiler.

🔥Advantages of Fire Tube Boiler🔥

1. Compact in construction.
2. Fluctuation of steam demand can be met easily.
3. Cheaper than water tube boiler.

🔥Disadvantages of Fire Tube Boiler🔥

1. Due to large water the required steam pressure rising time quite high.
2. Output steam pressure cannot be very high since the water and steam are kept in same vessel.
3. The steam received from fire tube boiler is not very dry.
4. In a fire tube boiler, the steam drum is always under pressure, so there may be a chance of huge explosion which resulting to severe accident.

2️⃣ PACKAGED BOILER

♨️Packaged boilers are company-made plug-and –play types of units.

♨️They have inherent advantages like compactness, short, easy operation, and hence, they are preferred   in process industries.

♨️Packaged boilers are generally of shell type with a large number of small- diameter tubes resulting in faster evaporation due to rate of convective heat transfer.Steam parameters vary from 10 bar saturated to 100 bar, 550 deg C.

♨️Further classification of packaged boilers includes number of passes of flue gas.

♨️Package boilers are fired from fuel oil in the form of liquid or gas. Fuel is ignited in the burners which creates an explosion within the boiler. Such package boiler do not require purifiers (filters) because they burn consistently removing all contaminants within the fuel. 

♨️To create constant combustion within the boiler, the forced draft fan forces air into the burner, causing a tornado effect creating turbulence to keep the flame ignited and the furnace pressurized. 

♨️Other essentials such as Burner electronics provide auto-ignition and on-demand lighting feature that monitors the flame and pressure within the boiler. tube boiler Package boilers are commonly called water or fire tube Boilers. 

♨️Water tube boilers use convection heating, which draws the heat from the fire source, and passes against the generating tubes of the boiler, causing water inside those tubes to boil off into steam.

 ♨️The fire tube boiler arrangement utilizes conduction heating which transfers heat from physical contact. Fire tube boilers are not commonly used due to their method of conduction heating because pipes in direct contact with fire and cold water could damage the pipes. ♨️The package boiler is usually a two or three-pass fire-tube boiler with an internal furnace tube. This is similar to the much earlier Scotch boiler.

3️⃣ WATER TUBE BOILER

♨️The tubes extend between an upper header, called a steam drum, and one or more lower headers or drums.

♨️ Water tube boilers are designed to permit higher pressure and capacity. Because the pressure is confined inside the tubes, water tube boilers are fabricated in larger sizes compare to fire tube boilers.

♨️The prime advantage of a water-tube boiler is it can burn almost any solid, liquid, or gaseous fuel.

♨️Apart from common fuels, other fluids like biomass, Municipal Solid Waste (MSW), Tire Derived Fuel (TDF), and Refuse-Derived Fuel(RDF) can be used.

♨️ Another advantage of water-tube boilers withstand very high pressure and temperature, respond quickly to change in demand, expand and contract more easily than fire tube boilers, and due to this, generally have a longer service life.

♨️A high pressure watertube boiler (also spelled water-tube and water tube) is a type of boiler in which water circulates in tubes heated externally by the fire. 

♨️Fuel is burned inside the furnace, creating hot gas which heats water in the steam-generating tubes. In smaller boilers, additional generating tubes are separate in the furnace, while larger utility boilers rely on the water-filled tubes that make up the walls of the furnace to generate steam.

♨️The heated water then rises into the steam drum. Here, saturated steam is drawn off the top of the drum. In some services, the steam will reenter the furnace through a superheater to become superheated.

 ♨️Superheated steam is defined as steam that is heated above the boiling point at a given pressure. Superheated steam is a dry gas and therefore used to drive turbines, since water droplets can severely damage turbine blades.

♨️Cool water at the bottom of the steam drum returns to the feedwater drum via large-bore 'downcomer tubes', where it pre-heats the feedwater supply. (In large utility boilers, the feedwater is supplied to the steam drum and the downcomers supply water to the bottom of the waterwalls). 

♨️To increase economy of the boiler, exhaust gases are also used to pre-heat the air blown into the furnace and warm the feedwater supply. Such watertube boilers in thermal power stations are also called steam generating units.

♨️The older fire tube boilers design, in which the water surrounds the heat source and gases from combustion pass through tubes within the water space, is a much weaker structure and is rarely used for pressures above 2.4 MPa (350 psi). 

♨️A significant advantage of the watertube boiler is that there is less chance of a catastrophic failure: there is not a large volume of water in the boiler nor are there large mechanical elements subject to failure.

♨️A water tube boiler was patented by Blakey of England in 1766 and was made by Dallery of France in 1780.

♨️The main disadvantage is initial cost due to more sophisticated construction.

The three major configuration of water tube boilers are

👉Straight-tube longitudinal drum

👉Straight-tube cross drum 

👉Stiriling boiler

☝️STIRLING BOILER DIAGRAM☝️

5️⃣ STOKER FIRED BOILER

♨️Stroke fired boiler have a mechanical system designed to feed solid fuel into the boiler.

♨️These stokers are designed to support combustion process and to remove ash as it accumulates.

♨️Modern mechanical strokes includes

♀️A fuel admission system

♀️A stationary or moving grate assembly that supports the burning of fuel and provides a pathway for the primary combustion air

♀️A secondary air in system that supplies additional air for complete combustion and minimize atmospheric emissions and

an ash-discharge system. 

♨️Stoker Fired Boiler are classified according to the method of feeding fuel to the furnace and by the type of grate. The main types of stokers are:

1. Chain-grate or travelling-grate stoker

♨️In Travelling Grate  boiler coal is fed at one end of a moving steel chain grate. As grate moves along the length of the boiler furnace, the coal burns before dropping off at the end as ash. 

♨️Some degree of skill is required, particularly when setting up the grate, air dampers and baffles, to ensure clean combustion leaving minimum of unburnt carbon in the ash.

♨️The coal-feed hopper runs along the entire coal-feed end of the furnace. A coal grate is used to control the rate at which coal is fed into the furnace, and to control the thickness of the coal bed and speed of the grate. 

♨️Coal must be uniform in size, as large lumps will not burn out completely by the time they reach the end of the grate. 

♨️As the bed thickness decreases from coal-feed end to rear end, different amounts of air are required more quantity at coal-feed end and less at rear end. 

2.Spreader stoker boiler

♨️Spreader stokers utilize a combination of suspension burning and grate burning. The coal is continually fed into the furnace above a burning bed of coal. 

♨️The coal fines are burned in suspension; the larger particles fall to the grate, where they are burned in a thin, fastburning coal bed. 

♨️This method of firing provides good flexibility to meet load fluctuations, since ignition is almost instantaneous when firing rate is increased. Hence, the spreader stoker is favored over other types of stokers in many industrial applications.♨️Spreader feeders have the capability to uniformly feed coal into a device that can propel it along the depth of a grate in an evenly distributed pattern. Many designs have been used successfully over the years. 

♨️The coal feed mechanisms include gravity reciprocating plates and metering chain conveyors. The mechanisms that propel the coal into the furnace include steam and air injection as well as underthrow and overthrow rotors. Steam or air assist can be used with the rotor systems.

♀️It can be further classified as either underfeed or overfeed stokers.

👉Underfeed stokers. 

👉Overfeed stokers.

👉Mass-feed stokers

👉Spreader stokers

7️⃣ PULVARIZED COAL BOILER

♨️The pulverized coal boiler is the most favourite method of burning coal.

In this, coal mechanically pulverized into a fine powder, which enables it to burn like gas and allow more efficient combustion. Many water tube boilers  use pulverized fuel in which coal is crushed to a powder form so that less than 2% is +300µm size and 75% is -75µm size.

♨️Pulverized coal is supplied with primary air to the burners.

♨️The main advantage is of quick response to load  variation  and ability to use high preheat air Temperature. 

The concept of burning coal that has been pulvarized into a fine powder stems from the belief that if the coal is made fine enough, it will burn almost as easily and efficiently as a gas. The feeding rate of coal according to the boiler demand and the amount of air available for drying and transporting the pulverized coal fuel is controlled by computers. Pieces of coal are crushed between balls or cylindrical rollers that move between two tracks or "races." 

♨️The raw coal is then fed into the pulvarizer along with air heated to about 650°F / 340°C from the boiler. As the coal gets crushed by the rolling action, the hot air dries it and blows the usable fine coal powder out to be used as fuel. The powdered coal from the pulverizer is directly blown to a burner in the boiler. 

♨️The burner mixes the powdered coal in the air suspension with additional pre-heated combustion air and forces it out of a nozzle similar in action to fuel being atomized by a fuel injector in modern cars. ♨️Under operating conditions, there is enough heat in the combustion zone to ignite all the incoming fuel. 

🔥ASH REMOVAL🔥

♨️There are two methods of ash removal at furnace bottom:

• Dry bottom boiler
• Wet bottom boiler, also called Slag tap

♨️The fly ash is carried away with the flue gas and is separated in various hoppers in the path and finally in an ESP or a bag filter.

8️⃣ FLUIDIZED BED BOILER

♨️Fluidized- bed combustion boilers are capable of burning a variety of solid fuels including biomass fuel.

♨️ As shown in figure, the fuel burns in a bed of hot incombustible particles suspended by an upward flow of air. The advantage of FBC boiler is that fuels containing high concentration of ash, sulphur and nitrogen burn efficiently with lower emission levels. 

♨️To start FBC boilers, natural gas or fuel oil is used.

♨️Advantage of FBC boilers are combustion takes place at relatively lower temperature which results in lower NO2 emission and reduced slag information; another advantage is limestone added to the fluidized bed helps to remove sulphur. 

♨️In its most basic form, fuel particles are suspended in a hot, bubbling fluidity bed of ash and other particulate materials (sand, limestone etc.) through which jets of air are blown to provide the oxygen required for combustion or gasification. ♨️The resultant fast and intimate mixing of gas and solids promotes rapid heat transfer and chemical reactions within the bed. 

♨️FBC plants are capable of burning a variety of low-grade solid fuels, including most types of coal and woody biomass, at high efficiency and without the necessity for expensive fuel preparation (e.g., pulvarizing). In addition, for any given thermal duty, FBCs are smaller than the equivalent conventional furnace, so may offer significant advantages over the latter in terms of cost and flexibility.

♨️FBC reduces the amount of sulphur emitted in the form of sulphur dioxide emissions. Limestone is used to precipitate out sulfate during combustion, which also allows more efficient heat transfer from the boiler to the apparatus used to capture the heat energy (usually water tubes).

 ♨️The heated precipitate coming in direct contact with the tubes (heating by conduction) increases the efficiency. Since this allows coal plants to burn at cooler temperatures, less nitrogen dioxide is also emitted. 

♨️However, burning at low temperatures also causes polycyclic aromatic hydrocarbon emissions. FBC boilers can burn fuels other than coal, and the lower temperatures of combustion (800 °C / 1500 °F) have other added benefits as well.

🔥BENEFITS OF FLUIDIZED BED BOILER

♨️There are two reasons for the rapid increase of FBC in combustors. First, the liberty of choice in respect of fuels in general, not only the possibility of using fuels which are difficult to burn using other technologies, is an important advantage of fluidized bed combustion. ♨️The second reason, which has become increasingly important, is the possibility of achieving, during combustion, a low emission of nitric oxides and the possibility of removing sulfur in a simple manner by using limestone as bed material.

♨️Fluidized-bed combustion evolved from efforts to find a combustion process able to control pollutant emissions without external emission controls (such as scrubbers-flue gas desulfurization).

♨️ The technology burns fuel at temperatures of 1,400 to 1,700 °F (750-900 °C), well below the threshold where nitrogen oxides form (at approximately 2,500 °F / 1400 °C, the nitrogen and oxygen atoms in the combustion air combine to form nitrogen oxide pollutants); 

♨️it also avoids the ash melting problems related to high combustion temperature. The mixing action of the fluidized bed brings the flue gases into contact with a sulphur-absorbing chemical, such as limestone or dolomite. More than 95% of the sulfur pollutants in coal can be captured inside the boiler by the sorbent. ♨️The reductions may be less substantial than they seem, however, as they coincide with dramatic increases in polycyclic aromatic hydrocarbons, and possibly other carbon compound emissions.

♨️Commercial FBC units operate at competitive efficiencies, cost less than today's conventional boiler units, and have SO₂ and NO₂ emissions below levels mandated by Federal standards. 

♨️However, they have some disadvantages such as erosion on the tubes inside the boiler, uneven temperature distribution caused by clogs on the air inlet of the bed, long starting times reaching up to 48 hours in some cases.

1. FBC has a lower combustion temperature of 750 °C whereas an ordinary boiler operates at 850 °C.
2. FBC has low sintering process (melting of Ash).
3. Lower production of NO_x due to lower temperature.
4. Lower production of SO_x due to capture by limestone.
5. Higher combustion efficiency due to 10 times more heat transfer than other combustion processes because of burning particle.
6. Less area is required for FBC due to high coefficient of convective heat transfer.
7. Iso-thermal bed combustion as temperature in free belt and active belt remain constant.

🔥TYPES OF FLUIDIZED BED BOILERS 🔥

♨️FBC systems fit into essentially two major groups, atmospheric systems (FBC) and pressurized systems (PFBC), and two minor subgroups, bubbling (BFB) and circulating fluidized bed (CFB).

🔥Fluidized Bed Combustible🔥

♨️Atmospheric fluidized beds use limestone or dolomite to capture sulfur released by the combustion of coal.

 ♨️Jets of air suspend the mixture of sorbent and burning coal during combustion, converting the mixture into a suspension of red-hot particles that flow like a fluid. These boilers operate at atmospheric pressure.

🔥Pressurized Fluidized Bed Combustion🔥

♨️The first-generation PFBC system also uses a sorbent and jets of air to suspend the mixture of sorbent and burning coal during combustion. 

♨️However, these systems operate at elevated pressures and produce a high-pressure gas stream at temperatures that can drive a gas turbine . 

♨️Steam generated from the heat in the fluidized bed is sent to a steam turbine , creating a highly efficient combined cycle system.

🔥Advanced PFBC🔥

• A 1½ generation PFBC system increases the gas turbine firing temperature by using natural gas in addition to the vitiated air from the PFB combustor. This mixture is burned in a topping combustor to provide higher inlet temperatures for greater combined cycle efficiency. However, this uses natural gas, usually a higher priced fuel than coal.
• APFBC. In more advanced second-generation PFBC systems, a pressurized carbonizer is incorporated to process the feed coal into fuel gas and char. The PFBC burns the char to produce steam and to heat combustion air for the gas turbine. The fuel gas from the carbonizer burns in a topping combustor linked to a gas turbine, heating the gases to the combustion turbine's rated firing temperature. Heat is recovered from the gas turbine exhaust in order to produce steam, which is used to drive a conventional steam turbine, resulting in a higher overall efficiency for the combined cycle power output. These systems are also called APFBC, or advanced circulating pressurized fluidized-bed combustion combined cycle systems. An APFBC system is entirely coal-fueled.
• GFBCC. Gasification fluidized-bed combustion combined cycle systems, GFBCC, have a pressurized circulating fluidized-bed (PCFB) partial gasifier feeding fuel synhas to the gas turbine topping combustor. The gas turbine exhaust supplies combustion air for the atmospheric circulating fluidized-bed combustor that burns the char from the PCFB partial gasifier.
• CHIPPS:A CHIPPS system is similar, but uses a furnace instead of an atmospheric fluidized-bed combustor. It also has gas turbine air preheater tubes to increase gas turbine cycle efficiency. CHIPPS stands for combustion-based high performance power system.