# General Custemis Steam  Boiler

#### A student’s scientific work can be used as a reference for knowledge about boilers in general. Knowledge of the types of boilers can be found in this paper. How it works and some calculations of calories produced or lost during operation.

CHAPTER I

PRELIMINARY

1.1  Background

In this modern era there are many things that we must know so as not to be left behind by others especially, developing countries like Malaysia, with this, I provide knowledge which might be beneficial for all, here I will give knowledge about tools, namely Boilers, wherein the definition of boiler here is a closed vessel where it is released into the water until hot water and steam are formed Hot water or steam at a certain pressure is then used to flow heat to a process. Water is a useful and inexpensive medium for delivering heat to a process. If water is boiled to steam, the volume will increase by about 1,600 times, producing energy that resembles explosive gunpowder, so that the boiler is equipment that must be managed and maintained very well.

1.2. Formulation of the problem

Based on the background described above, it was formulated

As follows:

1. Types of boilers
2. Boiler efficiency
3. Energy efficiency opportunities
4. Boiler checklist

1.3. Purpose of the Paper

The purpose of this paper was as one of the requirements for the completion of the Thermodynamics II course and to help provide information on knowledge, especially in the field of boilers and their uses.

CHAPTER II

BOILER

Boilers are closed vessels where combustion heat is flowed into the water until hot water or steam is formed . Hot water or steam at a certain pressure is then used to flow heat to a process. Water is a useful and inexpensive medium for delivering heat to a process. If water is boiled to steam , the volume will increase by about 1,600 times, producing energy that resembles explosive gunpowder, so that the boiler is equipment that must be managed and maintained very well.

The boiler system consists of: feed water system, steam system and fuel system. The feed water systemprovides water for the boiler automatically according to steam requirements . Various faucets are provided for maintenance and repair purposes. The steam system collects and controls steam production in the boiler. Steam is flowed through the piping system to the user’s point. In the whole system, steam pressure is regulated using a tap and monitored with a pressure monitor. Fuel systemare all equipment used to provide fuel to produce the heat needed. Equipment needed in the fuel system depends on the type of fuel used in the system.

The water supplied to the boiler to be converted into steam is called feed water . Two feed water sources are:

1. Condensate or condensing steam which returns from the process and
2. Air makeup (treated raw water) which must come from outside the boiler room and plant processes.

To obtain a higher boiler efficiency, an economizer is used to preheat feed water using waste heat in the exhaust gas.

1.    Types of boilers

Boilers consist of various types, namely:

1.  Fire Tube Boiler

In a fire tube boiler , hot gas passes through the pipes and boiler feed water is inside the shell to be converted into steam . Fire tube boilers are usually used for relatively small steam capacities with low to moderate steam pressures . As a guideline, competitive fire tube boilers for steam speeds up to 12,000 kg / hour with pressures up to 18 kg / cm 2 . Fire tube boilers can use fuel oil, gas or solid fuel in their operations. For economical reasons, most fire tube boilers constructed as a “package” boiler (assembled by the factory) for all fuels.

Figure 1. Fire Tube Boiler

1. WaTube Boiler

In the water tube boiler , boiler feed water flows through the pipes into the drum. The circulated water is heated by the combustion gas to form steam in the steam area in the drum. This boiler is chosen if the steamdemand and steam pressure are very high as in the case of a boiler for power plants. A very modern water tube boiler designed with a steam capacity between 4,500-12,000 kg / hour, with very high pressure. Many water tube boilers are constructed in packages if fuel and gas are used. For water tube boilers that use solid fuel, it is not commonly designed in packages.

Characteristics of boiler water tube as follows:

•  Forced , induced and balanced drafts help to improve combustion efficiency
• Less tolerant of the quality of water produced from a water treatment plant
• Allows for higher levels of heat efficiency

Figure 2. Water Tube Boiler

1.  Boiler Package

Called a boiler package because it is available as a complete package. When sent to the factory, it only requires steam pipes, water pipes, fuel supplies and electrical connections to operate. The boiler package is usually a shell and tube type with a fire tube design with both heat transfer and high convection.

The characteristics of packaged boilers are:

Ø  § The small amount of combustion space and high heat released results in faster evaporation.

Ø  § The large number of small diameter pipes makes it have good convective heat transfer.

Ø   Forced or induced draft systems produce good combustion efficiency.

Ø  § A number of passes / passes produce better overall heat transfer.

Ø  § A higher level of thermal efficiency compared to other boilers .

The boilers are grouped based on the number of passes / trajectories , namely how many times the combustion gas crosses the boiler. The combustion chamber is placed as the first track after that, then one, two, or three sets of fire pipes. The most common boilers in this class are three- pass units with two sets of fire-tubes / fire pipes and exhaust gases coming out from behind the boiler.

Figure 3. Type of 3 Pass Boiler Package, Oil fuel

1. Combustion Boiler with Fluidized Bed (FBC)

Fluidized bed combustion (FBC) appears as a possible alternative and has significant advantages over conventional combustion systems and provides many advantages including a compact boiler design, flexible to fuel, high combustion efficiency and reduced emissions of harmful pollutants such as SOx and NOx. The fuel that can be burned in this boiler is coal, repellent goods from the washing place for clothes, rice husks, bagasse & other agricultural wastes. Fluidized bed boilers have a wide range of capacities which are between 0.5 T / hr to more than 100 T / hr.

When evenly distributed air or gas is passed up through a bed of solid particles such as sand supported by a fine filter, the particles will not be disturbed at low speeds. Once the air velocity gradually rises, a state is formed where particles are suspended in the air stream so that the bed is called “fluidized”. With the subsequent increase in air velocity, bubble formation, strong turbulence, rapid mixing and the formation of a tight bed surface occur . Bed solid particles display the properties of boiling liquids and look like fluids called  ” bubbling fluidized beds “” If the sand particles in the fluidized state are heated to the coal flame temperature, and coal is injected continuously into the bed , the coal will burn quickly and the bed reaches a uniform temperature. Fluidized bed (FBC) combustion takes place at a temperature of about 840 ° C to 950 ° C. Because this temperature is far below the fusion temperature of ash, the melting of ash and the problems associated with it can be avoided. The lower combustion temperature is achieved due to the high heat transfer coefficient as a result of rapid mixing in the fluidized bed and effective heat extraction from the bedthrough heat transfer on pipes and bed walls. The gas speed is reached between the minimum fluidization speed and the particle entry speed. This ensures stable bed operation and avoids carrying particles in the gas path.

1. Atmospheric Fluidized Bed Combustion (AFBC) Boilers

Most boilers that operate for this type are Atmospheric Fluidized Bed Combustion (AFBC) Boilers . This tool is only a conventional conventional boiler shell coupled with a fluidized bed combustor. Such a system has been installed combined with a conventional water tube boiler / water pipe boiler. Coal is crushed into sizes 1-10 mm depending on the level of coal and the type of air feeder to the combustion chamber. Atmospheric air which acts as fluidizing and combustion air, is put under pressure, after being preheated by fuel exhaust gas. Pipes in beds that carry water generally act as evaporators. The combustion gas product passes through the super heater part of the boiler then flows to the economizer , to the dust collector and air pre-heater before being discharged into the atmosphere.

1. Pressurized Fluidized Bed Combustion (PFBC) Boilers

In the Pressurized Fluidized bed Combustion (PFBC) type, a compressor supplies air Forced Draft (FD), and the burner is a pressurized tank. The heat released in the bed is proportional to the pressure of the bed so that the deep bed is used to extract large amounts of heat. This will increase the combustion efficiency and absorption of sulfur dioxide in the bed . Steam is produced in two pipe bonds, one in the bed and the other in the top. Hot gas from the chimney drives a power-generating gas turbine. The PFBC system can be used to generate cogeneration ( steam and electricity) or power plants with combined cycles (combined cycle ) . Combined cycle operations (gas turbines & steam turbines) increase overall conversion efficiency by 5 to 8 percent.

1. Atmospheric Circulating Fluidized Bed Combustion Boilers (CFBC)

In the circulation system, bed parameters are maintained to form a floating solid from the bed . The solid is lifted in a phase that is relatively dissolved in the solids lift, and a down-comer with a cyclone is a solid circulation flow. There is no steam generator pipe located in the bed . The generation and overheating of steam takes place in the convection, water wall, at the output of the riser . CFBC boilers are generally more economical than AFBC boilers, for applications in the industry it requires more than 75 – 100 T / hour steam. For large units, the higher the characteristics of the CFBC boiler furnace will provide better use of space, greater fuel particles, the residence time of absorbent materials for efficient combustion and greater SO 2 capture , and the easier the application of combustion techniques for control NO x than the AFBC steamgenerator .

Figure 4. CFBC Boiler

1. Stoker Fired Boilers

Stokers are classified according to the method of fuel feeding into the furnace and by the type of grate . The main classification is the spreader stoker and chain-gate or traveling-gate stoker.

Spreader stockers utilize a combination of combustion suspension and grate combustion . Coal is fed continuously to the furnace above the coal combustion bed . Fine coal is burned in suspension; larger particles will fall into the grate , where they will be burned in thin, fast burning coal beds . This combustion method provides good flexibility to load fluctuations, because ignition almost occurs quickly when the combustion rate increases. Because of this, spreader stoker is preferred over other stoker types in various applications in the industry.

• Chain-grate or traveling-grate stoker

Coal is fed to the tip of a moving steel grate . When the grate moves along the furnace, coal burns before falling on the tip as ash. Certain skill levels are needed, especially when adjusting the grate , air damper and baffles , to ensure clean combustion and produce as little as possible the amount of carbon that does not burn in ash. The coal feed hopper extends along the entire end of the coal feed on the furnace. A coal grate is used to control the speed of coal fed to the furnace by controlling the thickness of the bedfuel. The size of coal must be uniform because large chunks will not burn perfectly when they reach the end of the grate .

Figure 6. Traveling Grate Boiler

1. Pulverized Fuel Boiler

Most coal-fired power station boilers use fine coal, and many water pipe boilers in larger industries also use fine coal. This technology is well developed and throughout the world there are thousands of units and more than 90 percent of coal combustion capacity is this type.

For bituminous coal, coal is ground to fine powder, measuring +300 micrometers (µm) less than 2 percent and measuring below 75 microns by 70-75 percent. It should be noted that too fine powder will waste grinding energy. Conversely, a powder that is too coarse will not burn perfectly in the combustion chamber and cause greater losses because the material is not burned. The powdered coal is blown out with part of the combustion air into the boiler plant through a series of burner nozzles . Secondary and tertiary air can also be added. Combustion takes place at temperatures from 1300 – 1700 ° C, depending on the quality of the coal. Time of residence of particles in the boilerusually 2 to 5 seconds, and particles must be small enough for perfect combustion. This system has many advantages such as the ability to burn various coal qualities, a fast response to changes in load loads, the use of high preheated air temperatures etc. One of the most popular systems for fine coal combustion is tangential combustion using four burners from all four angles to create fireballs at the center of the furnace.

Figure 7. Tangential combustion for fine fuels

1. Hot Waste Boilers

Wherever waste heat is available at medium or high temperatures, waste heat boilers can be installed economically. If the steam needs more than the steam produced using hot exhaust gas, additional burnersthat use fuel can be used . If steam is not directly usable, steam can be used to produce electricity using a steam turbine generator. This is widely used in the reuse of heat from exhaust gases from gas turbines and diesel engines.

Figure 8. Simple scheme of Hot Waste Boilers

1. Thermic Fluid Heaters

At present, thermic fluid heaters have been used extensively in various applications for indirect heating processes. By using petroleum fluid as a heat transfer medium, the heater provides a constant temperature. The combustion system consists of a fixed grate with a mechanical draft arrangement . Modern thermic fluid oil-based heaters consist of a double coil, three- pass construction and are installed with a pressure jet system. The thermic fluid, which acts as a heat carrier , is heated in a heater and circulated through the user’s equipment. This fluid transfers heat to the process through a heat exchanger, then the fluid is returned to the heater. The thermic fluid flow at the end of the user is controlled by a pneumatically operated control valve, based on the operating temperature. Heaters operate on high or low fires depending on the temperature of the returning oil which varies depending on the system load.

The advantages of these heaters are:

• Closed system operation with minimum loss compared tosteam boiler .
• Non-pressurized system operation even for temperatures around 2500 C compared to 40 kg / cm 2 steampressure requirements in similar steam systems .
• Automatic control settings, which provide operating flexibility.
• Goodthermal efficiency due to the absence of heat loss caused byblowdown, condensate removal and flash steam .

The overall economic factor of a thermal fluid heater depends on the specific application and basis of reference. Coal-fired thermic fluid heaters with a 55-65 percent heat efficiency range are the most convenient to use compared to most boilers. Combining heat recovery equipment in exhaust gas will enhance the next thermal efficiency level.

Figure 9. Configuring a Thermic Fluid Heater

2.3 Assessment of boilers

This section explains the evaluation of the performance of boilers, blowdown boilers, and boiler water treatment.

2.3.1        Evaluation of boiler performance

Boiler performance parameters, such as efficiency and evaporation ratio, decrease with time due to poor combustion, dirty surface heat exchanger and poor operation and maintenance. Even for new boilers , reasons such as poor fuel quality and water quality can result in poor boiler performance. A heat balance can help in identifying heat losses that can or cannot be avoided. Boiler efficiency tests can help in finding boiler efficiency deviations from the best efficiency and target problem areas for corrective actions.

1. a)Hot balance

The combustion process in the boiler can be described in the form of an energy flow diagram. This diagram graphically illustrates how the incoming energy from fuel is converted into energy flows of various uses and becomes a flow of heat and energy loss. Thick arrows indicate the amount of energy contained in each stream.

Figure 10. Boiler energy balance diagram

The heat balance is the total energy balance that enters the boiler against the one leaving the boiler in a different form. The following figure illustrates the various losses that occur for steamgeneration .

Figure 11. Loss in Coal-fired Boilers

Energy loss can be divided into losses that cannot or can be avoided. The purpose of Cleaner Production and / or energy assessment must reduce avoidable losses, by increasing energy efficiency. The following losses can be avoided or reduced:

1. Chimney gas loss:
1.        – Excess air (down to the minimum value    depending on burner technology , operation (control), and  maintenance)
2.        – Chimney gas temperature (lowered by optimizing maintenance (cleaning), load; better burner and boiler technology)
1. Loss due to unburned fuel in chimneys and ash (optimizing operation and maintenance; better burnertechnology )
2. Loss from blowdown (processing of fresh feed water, condensate recycling)
3. Condensate loss (use as much condensate as possible)
4. Convection and radiation losses (reduced by better boiler insulation)

1. b) Boiler Efficiency

The efficiency of the thermic boiler is defined as the percent of energy (heat) in which is used effectively on the steam produced.

There are two methods for assessing boiler efficiency:

• Direct Method: energy obtained from working fluid (water andsteam )   compared to the energy contained in boiler fuel .
• Indirect Method: efficiency is the difference between loss and energy entering.

2.4 Direct methods for determining boiler efficiency

Methodology

Also known as the ‘method of input-output’ due to the fact that this method requires only the output / output(steam) and the heat / input (fuel) for evaluating the efficiency. This efficiency can be evaluated using the formula:

Boiler Efficiency ( h ) = Heat Exit x 100

Heat in

Boiler Efficiency ( h ) = Q x (h     g – h f )       x 100

qx GCV

The parameters monitored for calculating boiler efficiency with the direct method are:

• Amount of steam produced per hour (Q) in kg / hour
• Amount of fuel used per hour (q) in kg / hour
• Working pressure (in kg / cm2 (g)) and overheating temperature (oC), if any
• Feed water temperature (oC)
• Thetype of fuel and the gross heat value of fuel (GCV) in kcal / kgof fuel

Where

• hg – The value of saturated steam in kcal / kg steam
• hf – The quantity of feed water in kcal / kg of water

Example

Look for boiler efficiency with a direct method with the data given below:

• Coal-firedboiler types
• Amount of (dry) steam produced:                    10 TPJ
• Steam (gauge ) / temperature pressure :                                   10 kg / cm 2 (g) / 180 0 C
• Amount of coal usage:2.25 TPJ
• Feed water temperature:                                                        85 0 C
• Coal GCV:                                                           3200 kcal / kg
• Enthalpy of steam at a pressure of 10 kg / cm2 : 665 kcal / kg (saturated)
• Entalp of feedwater:                                                  85 kcal / kg

Boiler efficiency ( h ) = 10 x (665 – 85) x 1000 x 100 = 80.56 percent

2.25 x 3200 x 1000

• Factory workers can quickly evaluate boiler efficiency
• Requires a few parameters for calculation
• Requires a little instrument for monitoring
• Easy to compare evaporation ratios withbenchmark data

Direct method loss

• Does not give instructions to the operator about the causes of lower         system efficiency
• Not counting various losses that affect various levels of efficiency

2.5 Indirect methods of determining boiler efficiency

Methodology

The reference standard for in-place Boiler Test using indirect methods is British Standard, BS 845: 1987 and ASME PTC-4-1 USA Standard Power Test CodeSteam Generating Units .

Indirect methods are also known as the heat loss method. Efficiency can be calculated by subtracting the heat loss part from 100 as follows:

Boiler efficiency (n) = 100 – (i + ii + iii + iv + v + vi + vii)

Where the loss that occurs in the boiler is heat loss caused by:

1. Dry chimney gas
2. Evaporation of water formed due to H2 in fuel

iii. Evaporation of water content in fuel

1. The water content in combustion air
2. Fuel that does not burn infly ash
3. Fuel that does not burn inbottom ash

The loss caused by the water content in the fuel and caused by combustion of hydrogen depends on the fuel, and cannot be controlled by design.

Data needed for calculating boiler efficiency using indirect methods are:

• Ultimate fuel analysis (H 2 , O 2 , S, C, water content, ash content)
• Percentage of oxygen or CO2 in the exhaust gas
• Exhaust gas temperature ino C (Tf)
• Ambient temperature ino C (Ta) and air humidity in kg / kg of dry air
• GCV fuel in kcal / kg
• Percentage of material that can burn in ash (for solid fuels)
• GCV ash in kcal / kg (for solid fuels)

Detailed procedures for calculating boiler efficiency using indirect methods are given below. Usually, energy managers in the industry prefer simpler calculation procedures.

Stage 1: Calculate theoretical air requirements

= [(11.43 x C) + {34.5 x (H2 – O2 / 8)} + (4.32 x S)] / 100 kg / kg of fuel

Stage 2: Calculate the percent excess air supplied (EA)

percent O 2 x 100

=      ——————

(21 – percent O 2 )

Step 3: Calculate the actual air mass supplied / kg of fuel (AAS)

= {1 + EA / 100} x theoretical air

Stage 4: Estimating all heat loss

1.  Percentage of heat loss caused by dry exhaust gas

=  mx C p x (T f -T a ) x 100

—————————-

Fuel GCV

Where, m = mass of dry exhaust gas in kg / kg of fuel

m = (mass of dry combustion / kg of fuel) + (mass N 2

in fuel on a base of 1 kg) + (mass N 2 in                 the actual supply air mass ).

Cp = Flue gas heat (0.23 kcal / kg)

1. Percentage heat loss due to evaporation of water formed due to H2 in fuel

9 x H 2 {584 + C p (T f- T a )} x 100

=  ————————————–

Fuel GCV

Where, H 2 = percent H 2 in 1 kg of fuel

Cp = superheated steam heat (0.45 kcal / kg)

iii. Percent of heat loss due to evaporation of water content in the fuel

=   M {584+ C p (T f -T a )} x 100

———————————

Fuel GCV

Where, M-percentage of water content in 1 kg of fuel

Cp = superheated steam heat (0.45 kcal / kg)

1. Percent loses heat due to water content in the air

=    AAS x moisture factor x C p (T f -T a )} x 100

————————————————– –

Fuel GCV

Where, Cp = heat of superheated steam              (0.4 kcal / kg)

1. Percentage heat loss due to unburnt fuel in fly ash / fly ash

= Total collected ash / kg of burning fuel x GCV fly ash x 100

————————————————– —————————————

Fuel GCV

1. Percent of heat loss because the fuel is not burned inbottom ash

= Total collected ash per kg of burning fuel x GCV under x 100 ash

————————————————– —————————————

Fuel GCV

vii. Percent of heat loss due to radiation and other  countless losses .

Actual radiation and convection losses are difficult to assess because of the variety of surface emissivity, slope, airflow pattern, etc. In relatively small boilers, with a capacity of 10 MW, countless radiation losses can reach 1 to 2 percent of the gross calorific value of fuel, while the 500 MW boiler is 0.2 to 1 percent. Losses can be assumed to be exact depending on surface conditions.

Stage 5: Calculate boiler efficiency and boiler evaporation ratio

Boiler  efficiency (n) = 100 – (i + ii + iii + iv + v + vi + vii)

Evaporation Ratio = Heat used for steam / heat generation

The evaporation ratio is the kilogram of steam produced per kilogram of fuel used. The example is:

ü  Coal-fired boilers: 6 (i.e. 1 kg of coal can  produce 6 kg of steam)

ü  Boilers are fuel oil: 13 (i.e. 1 kg of coal can produce 13 kg of steam)

However, the evaporation ratio will depend on the type of boiler, fuel calorific value and efficiency.

Example

• Boilertype : Oil-fired
• Ultimateoil fuel analysis

C: 84 percent

H 2 : 12.0 percent

S: 3.0 percent

O 2 : 1 percent

• GCV Fuel oil:                                           10200 kcal / kg
• Oxygen: 7 percent
• Percentage of CO2: 11 percent
• Exhaust gas temperature (Tf):                                           220 0C
• Ambient temperature (Ta):                                               27 0C
• Air humidity: 0.018 kg / kg dry air

Stage 1: Calculate theoretical air requirements

= [(11.43 x C) + [{34.5 x (H 2 – O 2 /8)} + (4.32 x S)] / 100 kg / kg of fuel oil

= [(11.43 x 84) + [{34.5 x (12 – 1/8)} + (4.32 x 3)] / 100 kg / kg of fuel oil

= 13.82 kg of air / kg of fuel oil

Stage-2: Calculate percent of excess air supplied (EA)

Supplied excess air (EA)

=  (O 2 x 100) / (21-O 2 )

=  (7 x 100) / (21-7)

=   50%

Step 3: Calculate the actual air mass supplied / kg of fuel (AAS)

AAS / kg of fuel = [1 + EA / 100] x Theoretical Air (AAS)

= [1 + 50/100] x 13.82

= 1.5 x 13.82

= 20.74 kg of air / kg of fuel oil

Stage 4: Estimating all heat loss

1. Percentage of heat loss due to chimney dry gas

mx Cp x (Tf – Ta) x 100

=    —————————–

Fuel GCV

m = mass CO 2 + mass SO 2 + mass N 2 + mass O 2

0.84 x 44      0.03 x 64      20.74 x 77

m = ———–  +  ———-   +  ———–    (0.07 x 32)

12              32                100

m = 21.35 kg / kg of fuel oil

21.35 x 0.23 x (220-27)

=   ——————————- x 100

10200

=  9.29%

Percentage of heat loss caused by chimney dry gas

mx Cp x (Tf – Ta) x 100

=   —————————–

Fuel GCV

m (total mass of exhaust gas)

= actual air mass supplied + mass of fuel

supplied

= 20.19 + 1 = 21.19

= 21.19 x 0.23 x (220-27)

——————————- x 100

10200

= 9.22%

1. Heat loss due to evaporation of water formed due to H2 in the material

burn

9 x H 2 {584 + 0.45 (Tf – Ta)}

=  ———————————

Fuel GCV                       where H 2 = percent H 2 in fuel

9 x 12 {584 + 0.45 (220-27)}

=  ——————————–

10200

=  7.10%

iii. Heat loss due to moisture content in the air

AAS x humidity x 0.45 x ((Tf – Ta) x 100

=  ————————————————-

Fuel GCV

= [20.74 x 0.018 x 0.45 x (220-27) x 100] / 10200

= 0.317%

1. Heat loss due to radiation and countless other losses

For small boilers it is estimated that the loss reaches 2%

Stage 5: Calculate boiler efficiency and boiler evaporation ratio

Boiler efficiency (n) = 100 – (i + ii + iii + iv + v + vi + vii)

ü    Heat loss due to dry exhaust gas                                   : 9.29%

ü               Heat loss due to evaporation of water formed due to the presence of H2

in fuel                                            : 7.10%

ü  Heat loss due to moisture content in the air : 0.317%

ü  Heat loss due to radiation and countless other losses

: 2%

= 100- [9.29 + 7.10 + 0.317 + 2]

= 100 – 17,024 = 83% (estimated)

Evaporation ratio = Heat used for steam / heat generation

= 10200 x 0.83 / (660-60)

= 14.11 (compare with the evaporation ratio for boilers made from

fuel oil = 13)

• Complete material and energy balance can be known for each flow, which can make it easier to identify options to improve boiler efficiency.

Indirect method losses

• Takes a long time
• Requires laboratory facilities for analysis

2.6. Blowdown Boiler

If water is boiled and steam is produced , dissolved solids contained in the water will stay in the boiler. If a lot of solids are contained in feed water, the solids will be concentrated and eventually will reach a level where the solubility in the water will be exceeded and will settle from the solution. Above a certain level of concentration, the solids encourage the formation of foam and cause the water to be carried away to steam . The sediment also results in the formation of a crust inside the boiler, resulting in overheating and eventually causing failure of the boiler pipe.

Therefore it is important to control the level of concentration of solids in the suspension and those dissolved in boiled water. This is achieved by a process called blowing down , where a certain amount of water volume is released and automatically replaced with feed water. Thus an optimum level of total dissolved solids (TDS) will be achieved in boiler water and dispose of evenly solids out of the solution and which tend to stay on the boiler surface.

Blowdown is important to protect the heat exchanger surface of the boiler. However, blowdown can be a significant source of heat loss, if done incorrectly. Good control of boiler blowdown can significantly reduce the treatment and operational costs that cover :

Ø  Lower initial treatment costs

Ø  The consumption of water make-up less

Ø The  time of termination for treatment is reduced

Ø  The life of the boiler increases

Ø The  use of chemicals for processing feed water is lower

2.7.  Boiler Feed Water Treatment

Producing quality steam depends on proper water treatment to control steam purity , sediment and corrosion. A boiler is part of a boiler system, which receives all pollutants from the system in front of it. Boiler performance, efficiency, and service life are the direct results of selecting and controlling feed water used in boilers.

If the feed water enters the boiler, the increase in temperature and pressure causes the water component to have different properties. Almost all components in feed water are dissolved. However, under heat and pressure almost all dissolved components come out of the solution as particulate solids, sometimes in crystal form and at other times as amorphous forms If the solubility of a specific component in water is exceeded, crust and sediment formation will occur. Boiler water must be sufficiently free from the formation of solid deposits so that rapid and efficient heat transfer occurs and must not be corrosive to the boiler metal.

1. a) Sediment control

Deposits in boilers can result from hardness of feed water and corrosion results from condensate and feed water systems. Hardness of feed water can occur due to a lack of softening systems. Imposing and corrosion causes loss of efficiency which can cause failure in boiler pipes and inability to produce steam . The precipitate acts as an insulator and slows down heat transfer. A large amount of deposits throughout the boiler can reduce heat transfer which can significantly reduce boiler efficiency. Different types of deposits will affect boiler efficiency differently, so it is very important to analyze sediment characteristics. The effect of isolating against deposits causes an increase in boiler metal temperature and may cause pipe failure due to overheating.

1. b) Dirt that results in precipitation

The most important chemicals in water that affect the formation of deposits in boilers are calcium and magnesium salts known as hard salt.

Calcium and magnesium bicarbonate dissolve in water to form alkaline / alkaline solutions and these salts are known as alkali hardness. The salts decompose by heating, releasing carbon dioxide and forming soft mud, which then settles. This is called temporary hardness (hardness that can be removed by boiling).

Calcium and magnesium sulfate, chloride and nitrate,   if chemically dissolved in water will be neutral and are known as non-alkali hardness. These materials are called permanent hard chemicals and form hard crust on the surface of the boiler which is difficult to remove. Non-alkali-containing chemicals are released from the solution because of a decrease in solubility with increasing temperature, by concentrating due to evaporation that takes place in the boiler, or by changing chemicals into less soluble compounds.

1. c) Silica

The presence of silica in boiler water can increase the formation of hard silica scale. Silica can also interact with calcium and magnesium salts, form calcium silicate and magnesium with low thermal conductivity. Silica can increase deposits on the turbine fins, after being carried in the form of deep water droplets

steam , or in the form of volatile in steam at high pressure.

1. d) Internal water treatment

Internal processing is the addition of chemicals to the boiler to prevent the formation of scale. Crust forming compounds are converted into free flowing mud, which can be removed by blowdown . This method is limited to boilers where feed water contains low hardness salts, with low pressure, high TDS content in the boiler can be tolerated, and if the amount of water is small. If these conditions are not met, a high blowdown rate is needed to remove the sludge. This becomes uneconomical due to loss of water and heat.

Different types of water sources require different chemicals. Compounds such as sodium carbonate, sodium aluminate, sodium phosphate, sodium sulfite and components of vegetables or inorganic compounds can all be used for this purpose. For each water condition certain chemicals are needed. A specialist must be consulted in determining which chemicals are most suitable for use in each case. Water treatment only with internal processing is not recommended.

1. e) External Water Treatment

External processing is used to remove suspended solids, soluble solids (especially calcium and magnesium ions which are the main causes of crust formation) and dissolved gases (oxygen and carbon dioxide).

The existing external treatment process is:

• Ion exchange
• Deaeration (mechanical and chemical)
• osmosis (reverse osmosis )
• Mineral removal / demineralization

Before using the method above, it is necessary to remove solids and colors from the raw material of water, because the material can contaminate the resin used in the next processing section.

The initial treatment method is simple sedimentation in settling or precipitation tanks in clarifierswith the help of coagulants and flocculants. Pressurized sand filters, with aeration to remove carbon dioxide and iron, can be used to remove metal salts from well water.

The first stage of processing is removing hard salt and non-hard salt. Removal of only hard salt is called softening, while the removal of total salt from the solution is called mineral removal or demineralization.

1. f) Recommendations for boilers and feed water quality

The dirt found in the boiler depends on the quality of unprocessed feed water, the processing used and the boiler operating procedures. As a general rule, the higher the boiler operating pressure, the greater the sensitivity to dirt.

2.8 Energy efficiency opportunities

This section contains opportunities for energy efficiency in relation to combustion, heat transfer, avoidable loss, energy consumption for auxiliaries, water quality and blowdown. Energy losses and energy efficiency money mops in boilers can be associated with combustion, heat transfer, avoidable loss, high energy consumption for auxiliary equipment, water quality and blowdown . Various kinds of energy efficiency opportunities in boiler systems can be connected with:

1.  Control the chimney temperature

The chimney temperature should be as low as possible. However, the temperature should not be too low so that moisture will condense on the chimney wall. This is important for fuels containing sulfur which at low temperatures will result in corrosion of sulfur dew points. Chimney temperatures greater than 200 ° C indicate the potential to reuse waste heat. This also indicates that crust formation has occurred in the displacement / heat utilization equipment and should be carried out earlier shut down for cleaning the water / chimney side.

1. Preheating feed water using economizers

Usually, exhaust gases leave a modern 3 pass shell boiler at a temperature of 200 to 300 ° C. So, there is the potential to reuse heat from these gases. The exhaust gas coming out of a boiler is usually maintained at a minimum of 200 ° C, so that sulfur oxide in the exhaust gas does not condense and cause corrosion on the heat transfer surface. If clean fuels such as natural gas, LPG or oil gas are used, the economy of heat recovery must be determined as the exhaust gas temperature may be below 200 ° C.

The potential for energy savings depends on the type of boiler installed and the fuel used. For older model shell boilers, with the chimney gas temperature exiting 260 ° C, an economizer must be used to reduce the temperature to 200 ° C, which will increase the feed water temperature by 15 ° C. The increase in thermal efficiency will reach 3%. For modern 3 pass shell boilers fueled with natural gas with a chimney gas temperature coming out of 140 ° C, a condensing economizer will reduce temperatures to 65 ° C and increase thermal efficiency by 5%.

1. Initial heating of combustion air

Initial heating of combustion air is an alternative to heating feed water. In order to increase thermal efficiency by 1 percent, the combustion air temperature must be increased by 20 ° C. Most fuel and gas oil burners used in a boiler plant are not designed for high air preheater temperatures.

Modern burners can withstand higher combustion air heaters, so it is possible to consider such units as heat exchangers in the exhaust gas, as an alternative to the economizer , if the space or temperature of the high feedwater is possible.

1.    Minimize incomplete combustion

Incomplete combustion can arise from lack of air or excess fuel or poor distribution of fuel. This is evident from the color or smoke, and must be corrected immediately. In oil and gas combustion systems, the presence of CO or smoke (only for oil combustion systems) with normal or very excessive air indicates the problem in the burner system Incomplete combustion due to poor mixing of air and fuel in the burner . The bad oil combustion can result from improper viscosity, damaged burner tip , carbonization at the burner tip and damage to diffusers or spinner plates .

In burning coal, unburned carbon can be a big loss. This occurs when carried by grit or the presence of carbon in ash and can reach more than 2 percent of the heat supplied to the boiler. The size of the fuel that is not uniform can also be the cause of incomplete combustion. In chain grate stokers , large chunks will not burn perfectly, while small and fine pieces will inhibit airflow, causing poor air distribution. At sprinkler stokers , stoker grate conditions, fuel distributors, air regulation and excessive combustion systems can affect carbon loss. Increasing fine particles in coal also increases carbon loss.

1.    Control of excess air

Excess air is needed in all combustion practices to ensure perfect combustion, to obtain combustion variations and to ensure a satisfactory chimney condition for some fuels. The optimal level of excess air for maximum boiler efficiency occurs when the amount of loss caused by incomplete combustion and loss caused by heat in exhaust gases is minimized. These levels vary depending on the furnace design, burner type , fuel and process variables.

Excessive air control at the optimal level always results in a decrease in loss of exhaust gas, for every 1 percent decrease in excess air there is an increase in efficiency of approximately 0.6 percent.

Various methods available to control excess air:

• Portableoxygen analyzers and draft gauges can be used to make periodic readings to guide the operator to manually adjust the airflow for optimum operation. An excess of 20 percent decrease in air is possible.
• The most common method is a continuous oxygen analyzer with direct reading in place, where the operator can adjust the air flow.A further decline of 10-15% can be achieved beyond the previous system.
• The same continuous oxygen analyzer can have apneumatic damper positioner that is controlled by a remote control device, where data readings are available in the control room. This makes the operator able to control a number of ignition systems remotely simultaneously.

The most advanced system is controlling the automatic chimney damper , which is because the price is only for large systems.

1. Avoidance of radiation heat and convection loss

The outer surface of the boiler shell is hotter than the surroundings. So, the surface releases heat to the environment depending on the surface area and the temperature difference between the surface and the surrounding environment.

The heat lost from the boiler shell is usually a certain energy loss, regardless of the boiler output With a modern boiler design, this loss is only 1.5 percent of the gross heating value at full speed, but will increase to around 6 percent if the boiler operates only at 25 percent output. Repair or enlargement of insulation can reduce heat loss in the boiler walls and piping .

1.  Automatic blowdown control

Uncontrolled continuous blowdown is very futile. An automatic blowdown controller can be installed which is a sensor and responds to boiler water conductivity and pH. A 10 percent blowdown in a 15 kg / cm2 boiler results in a 3 percent efficiency loss.

1. Reduction of crust formation and loss of soot

In oil and coal-fired boilers, soot formed on pipes acts as an insulator against heat transfer, so the deposits must be   removed regularly. The increased chimney temperature can indicate excessive soot formation. The same results will also occur because of the formation of crust on the side of the water. The normal temperature of the gas coming out in excess air indicates a poor heat transfer performance. This condition can result from the gradual formation of deposits on the gas side or water side. The formation of deposits on the water side requires a review of the method of water treatment and pipe cleaning to remove deposits. An estimated 1 percent efficiency loss occurs at each chimney temperature rise of 22 ° C.

The temperature of the chimney should be checked and recorded regularly as an indicator of soot deposition. When the gas temperature rises to around 20 ° C above the temperature of the newly cleaned boiler, it is time to remove the soot deposits. Therefore it is recommended to install a dial type thermometer at the base of the chimney to monitor the temperature of the gas out of the chimney.

It is estimated that 3 mm of soot can result in a 2.5 percent increase in fuel consumption due to increased chimney gas temperatures. Periodic cleaning on the surface of radiant furnaces , boiler pipes , economizers and air heaters may be necessary to remove these difficult to remove deposits.

1. Reduction of steam pressure on the boiler

This is an effective way to reduce fuel consumption, if permitted, by 1 to 2 percent. Lower steampressure provides a lower saturated steam temperature and without the heat recovery of the chimney, which results in a decrease in temperature in the exhaust gas. Steam is produced at a pressure that matches the temperature / highest pressure for a particular process. In some cases, the process does not operate at all times and there is a period of time during which boiler pressure must be lowered. However, it must be remembered that the reduction in boiler pressure will reduce the specific volume of steam in the boiler, and effectively de-aerate the boiler output. If steam loadexceeded deheated boiler output, water transfer will occur. Therefore, energy managers must think about the consequences that might arise from the pressure reduction carefully, before recommending it. Pressure must be reduced gradually, and must be considered not to be more than 20 percent decrease.

1. Variable speed control for fans , blowers and pumps

A variable speed controller is an important way to get energy savings. Generally, control of combustion air is affected by damper closing valves mounted on forced fan and induced draft . Theprevious type of dampers is a simple control device, less precise, providing poor control characteristics in the upper and lower operating range. Generally, if the characteristics of the boiler load vary, the possibility of replacing the damper with VSD must be evaluated .

The maximum efficiency of the boiler does not occur at full load but at about two thirds of the full load. If the load on the boiler decreases, efficiency also tends to decrease. At zero output, the boiler efficiency is zero, and whatever the amount of fuel used is only to supply losses. The factors that affect boiler efficiency are:

• When the load falls, so does the value of the mass flow rate of the exhaust gas through the pipes.A decrease in flow rate for the same heat transfer area reduces the temperature of the exhaust gas out of the chimney in small amounts, reducing sensible heat loss .
• Theload is below half, almost most of the combustion equipment requires more excess air to burn fuel completely.This increases sensible heat loss .

Generally, boiler efficiency decreases below the 25 percent load rate and boiler operation below this level must be avoided as far as possible.

1.    Scheduling the right boiler

Because the optimum efficiency of the boiler occurs at 65-85 percent of full load, it is usually more efficient, overall, to operate fewer boilers at higher loads than to operate in large quantities at low loads.

1. Replacement of the boiler

The potential savings from replacing a boiler depend on the anticipated changes in overall efficiency. A change in the boiler can be financially attractive if the boiler is available:

• Old and inefficient
• Not able to replace cheaper fuel in combustion
• Thesize exceeds or below the existing requirements

The feasibility study must test all the long-term fuel implications and growth plans of the company. All financial and engineering factors must be considered. Because boiler plants traditionally have a service life of more than 25 years, replacement must be carefully studied.

CHAPTER III

BOILER CARE

3.1 BOILER CHECKLIST

This section involves the most common options for improving boiler energy efficiency.

3.1.1        Periodic tasks and inspection of the outside of the boiler

1. All entrances and plate connections must be kept airtight with an effective gasket
2.  All joint-pit connecting systems must be effectively closed and isolated if necessary
3. The boiler wall and its parts must be effectively insulated. Is the available insulation sufficient? If isolation of boilers, pipes and hot water cylinders a few years ago, this isolation is certainly too thin even if the insulation looks in good condition. Remember, this isolation is installed when fuel prices are still low. Increasing thickness may be needed.
4. At the end of the heating time, the boiler must be closed carefully, the inner surface that is open during the summer is covered with sheets that have desiccant inserts . (Only applicable to boilers that do not operate between heating seasons).

3.1.2        Boilers: Other things to increase steam and boiler hot water

• Check regularly the formation of crust or mud in the boiler tank or check the TDS of boiler water every shift, but not less than once per day. Impurities in boiler water are concentrated in the boiler and the limit depends on the type of boiler and the load. Boiler blowdown must be minimized, but must keep the water quality at the correct limit. Reuse heat from blowdown water .
• In steam boilers, is the water treatment sufficient to prevent foaming or priming and is the use of chemical ingredients not excessive?
• For steam boilers: does the water level controller operate? The existence of interconnected pipes can be very dangerous.
• Is it regularly checked for air leaks around the boiler inspection door, or between boilers and chimneys? The first can reduce efficiency, the next can reduce circulation and can encourage condensation, corrosion and dirt.
• The combustion conditions must be checked using a flue gas analyzer at least twice per season and the ratio of fuel / air must be set as needed.
• Detected and controlled places must be labeled effectively and checked regularly. The security lock must have a manual reset and alarm.
•   A test point must be available, or a permanent indicator device must be installed on the burner to see the pressure / temperature operating conditions.
•   In boilers that are oil or gas fueled, it is better to make a fuse box for cable connection systems that can be deadly in the event of fire or excessive heat on some trajectories that are passed by employees; the fuse box must be mounted as high as above the head height.
•   Deadly facilities in an emergency are placed at the exit of the boiler room.
•   To reduce corrosion, it must be maintained so that the temperature of condensate water returns far below the minimum dew point, especially in oil and coal-fired boilers.
• Users of fuel are very likely to have their own weigh bridges so that they can operate direct checks on shipments. If there is no weigh bridge, weighing can be done at the public weighbridge (or to the surrounding factory that has a weighbridge) just for inspection? For the delivery of liquid fuels it can be checked with a stick on the vehicle.
• In a boiler plant , it must be ensured that the fuel used is in accordance with the needs. In solid fuels, the correct quality or size is important, and the ash and moisture content must be planned in advance by the plant designer. In fuel oil, it must be ensured that the viscosity of the burner is correct, and the temperature of the fuel oil is also checked.
• Monitoring of fuel use must be as accurate as possible. Measurements on fuel inventories must be realistic. Energy Equipment
• In oil burners , it is best to check each part and repair it. The nozzle on the burner must be replaced regularly and carefully cleaned to prevent damage to the burner tip .
• Procedures for maintenance and repairs must be reviewed especially for burner equipment, control equipment and monitoring
• Regular cleaning of heat transfer surfaces maintains efficiency at the highest possible level.
• Must be assured that boiler operators are familiar with operating procedures especially for new control equipment.
•   Should we examine the possibility of reusing heat from the gases coming out of the boiler? Heat exchangers / recuperators are available for almost all types and sizes of boilers .
• Feed tanks and headers must be checked for any leaks in the make up faucet , correct isolation or loss of water in draining
• Tool manufacturers may have installed insulation on the boiler plant. Is insulation still enough for the current condition of fuel costs? Also checked the optimum thickness.
• If the amount of steam produced is too large, invest a steam gauge .
• Measure steam output and incoming fuel. The ratio of steam to fuel is the main measure of efficiency in the boiler .
•   Use the monitoring system provided: will display various signs of damage …
• Feed water must be checked regularly for quantity and purity.
•   The steam gauge must periodically be exposed to possible damage due to erosion in the measuring hole or pilot head . It must be noted that the steam gauge only provides correct readings at the calibrated steam pressure . Recalibration may be needed.
•   Check all pipelines, connections and steam traps from leaks, even in insufficient spaces
• Pipes that are not used must be separated and excessive pipes must be reduced
• A person must be appointed to operate and maintain after installation which must be included in the specifications of the work.
• Basic notes must be available to the person designated in the form of drawings, operation and maintenance orders in detail.
• The daily data record book must record in detail about the treatment performed, the reading of the combustion gases, weekly or monthly fuel consumption, and complaints that exist.
• Must be maintained so that steam pressure is no more than what is needed for work. When the material load at night is smaller than the load during the day, it is necessary to consider installing a pressure switch for pressure varying over a wider range at night to reduce the frequency of burner death , or limit the maximum burner burn rate .
• Checked boiler maintenance needs in standby conditions – here often occurs unexpected heat losses. Non -working boilers must be kept away from fluids and gas.
• Daily data that is good for boiler room activities must be available so that performance can be measured against the target. Burning checks, etc. with portable instruments , it must be done regularly,   boiler load conditions such as: percent CO2 at full / half load, etc. Must be recorded in the daily data book. Thermal Energy Equipment: Boilers & Thermal Fluid Heaters
•   Examination is done to ensure that severe fluctuations in load are not caused by improper operation of auxiliary equipment in boiler money, for example, ON / OFF controls for bait, faulty feed controller systems or incorrect design headers .
• Check doses of anti-corrosion additives for hot water heating systems every year to see that the concentration is still right. it is ensured that this additive is NOT included in the domestic hot water heater, because this will pollute the tap water.
• Reuse all condensate if possible in practice and if possible get savings.

3.2      Boiler room and plant room

>  Ventilation openings must be kept free and clean at all times and the opening area must be checked if they are sufficient.

>  Plant space should not be used for storage purposes, for wind or drying.

>  Have maintenance of pumps and automatic valves been carried out according to the manufacturer’s instructions?

>  Are the pumping and standby units alternating approximately once per month?

>  Are pump isolation valves available?

>  Are pressure / heat test points and / or indicators provided on each side of the pump?

>  Are pump casings provided with air release facilities? Are moving parts (eg couplings) protected?

>  Make sure that the accuracy of the instrument is checked regularly.

>   Visually inspect all pipe work and valves from various leaks.

>  Check that all security equipment is operating efficiently.

>  Check all electrical contacts to see that everything is clean and safe.

>   Ensure that all instruments are closed and safety guards are on

> the  place . Check all sensor devices, make sure they are clean, unobstructed and not open towards necessary conditions, for example the temperature sensor must not be exposed to direct sunlight, nor should it be placed near the heat pipe at the plant process.

>  Ensure that only authorized employees are allowed to enter control equipment.

>  Each part of the plant must operate if necessary, and should be controlled automatically.

>  Time control must be interconnected and the operation of the entire plant should be automatic.

> In installing multiple boilers, keep the boiler that is not needed on the water side and, if it is safe and possible, on the gas side. Make sure the boilers cannot burn.

>   Isolating the exhaust gas system (for protection) also reduces heat loss.

>  In installing multiple boilers, control of progress / delay must have a replacement facility.

>  Where possible, a reduction in the operating temperature of the system must be made using external equipment to the boiler and with the operation of the boiler below the normal constant temperature range.

3.3 Water and steam

Ø  Water fed to the boiler must meet the specifications provided by the manufacturer. Water must be clean, colorless and free of suspended dirt.

Ø  Zero hardness. Maximum 0.25 ppm CaCO3.

Ø  PH 8 to 10 slows down action or corrosion. pH less than 7 accelerates corrosion due to acid action.

Ø  Dissolved O2 is less than 0.02 mg / l. The presence of SO2 results in corrosion.

Ø  CO2 must be kept low. Its presence with O2 causes corrosion, especially in copper and bearings with copper mixed materials.

Ø  Water must be free of oil – this will cause priming.

3.4 Boiler water

1.  Water must be alkaline – below 150 ppm CaCO3 and above 50 ppm CaCO3 at pH 8.3 – The alkalinity / alkalinity value must be less than 120.
2.  The total solids must be kept below the value at which steam pollution is excessive, to avoid over-cooling and deposition hazards in overheating, steam pipelines and drive systems.
3.  Phosphate must be no more than 25 ppm P2 O5.
4.  The silica flower in the make-up feed water must be less than 40 ppm in boiler water and 0.02 ppm in steam, as SiO2. Large quantities can be carried into turbine blades

3.5 Blowdown  Procedure (BD)

Conventional and acceptable procedures for blowdown are as follows:

1. Close the water tap
2. Open the drain faucet (so that steam comes out freely)
3. Close the drain faucet
4. Close the steam faucet
5. Open the water tap
6. Open the drain faucet (so that steam comes out freely)
7. Close the drain faucet
8. Open the steam faucet
9. Open then close the drain faucet to the end of the blowdown process . The first water that appears usually represents boiler water If the water is colored, the cause must be found.