Boilers الغلايات

Boilers الغاليات

Submitted by:

Dr. Hazim Al-Jewaree

Steam Boiler Types

• Live steam models utilize many different varieties of boilers ranging from the simple pot to the locomotive type. Each boiler type can give excellent performance so long as it is operated within its design envelope. Copper is the best material for small boilers. Brass should never be used for a boiler barrel, but is satisfactory for fittings.

• Major boiler types are discussed as follows:

Pot Type

• The pot boiler, show in Figure 2, is the simplest type and consists of a cylindrical copper tube with stayed end plates. The fire, which is typically from an alcohol burner, is applied to the external surface of the boiler. Its steaming ability can be significantly increased by the addition of a smoke tube and a stainless steel shield which encloses the burner and the lower portion of the boiler. Thus configured, the pot boiler can be a god steam generator in moderate temperatures and mild winds.

Vertical Type

• The vertical boiler is a simple type which consists of a firebox at the bottom and a copper barrel with a smoke tube. It typically is used to drive stationary engines and boats. Firing is accomplished by alcohol or solid fuel pellets. More sophisticated versions of the vertical boiler contain many small tubes and are sometimes fired by coal or charcoal. (Fig. 3)

Center Flue Type • The center flue boiler, show in

Figure 4, has a large water capacity and a low center of gravity which makes it ideal for model boats. The center flue is surrounded by water and sometimes has several cross tubes to improve circulations. This type of boiler is usually fired by a gas burner, because the flame is completely enclosed by the center flue. Therefore, the probability of an accidental fire is reduced. It is necessary to maintain the proper water level in this type of boiler to avoid damaging the center flue. It offers good performance capabilities in adverse weather conditions.

Chemistry of Crude Oil• Thousands of hydrocarbons in oil, ranging from

light gases to heavy residues. Oils are different from each other in their physical properties and chemical compositions.

• Aliphatics: n-alkanes, branched-alkanes, cycloalkanes, and unsaturated aliphatics.

• Biomarkers: terpanes and steranes.• Aromatics: BTEX, Cn-benzenes, PAHs (3-6 rings).• Polars: S, N, and O-containing hydrocarbons.• Asphaltenes.• Metals.

The majority of crude oil is alkanes, cycloalkanes (naphthenes), aromatics,polycyclic aromatics, S-containing compounds, etc.Gasoline: branched alkanesDiesel: linear alkanes

Heavier crude contains more polycyclic aromaticsLead to carboneceous deposits called “coke”

Petroleum Refining

GAS

LIGHT NAPHTHA

HEAVY NAPHTHA

KEROSENE

ATM. GAS OIL

RESIDUUM

CRUDE DESALTER FURNACE

C1-C4

bp < 50 oF

C5 - C?

bp 50-200oF

C? - C12

bp 200-400oF

C12 - C16

bp 400-500oF

C15 - C18

bp 500-650oC

> C20

bp >650oF

TOWER

Distillation – separation by boiling point

Petroleum ReformingGAS

LIGHT NAPHTHA

HEAVY NAPHTHA

KEROSENE

ATM. GAS OIL

RESIDUUM

TOWER

FUEL GAS

TREATER

HYDROTREATER

HYDROTREATER

HYDROTREATER

REFORMER AROMATIC EXTRACTION

CATALYTICCRACKER

JET FUELS/KEROSENE

DIESEL & FUEL OILS

GASOLINE

AROMATICS

VacuumDistillation

VACUUM GAS OIL

LUBRICATING OIL

COKER COKE

ASPHALT

CATALYTICCRACKER

Thermal Power Stations

Note: thermal includes fossil-fuel and nuclear powerHeat source is part of Steam CycleThermodynamics of cycle independent of nature of heat source

Steam Cycle: Main Components

WaterPump

Boiler

Heat in

Turbine (expander)

Electrical powerCondenser

Cooling waterHeat out

Basic Hydrocarbon Families

Family name

Other designations

Molecular formula

Carbon-carbon bonding

Primary molecular structure

Alkanes Paraffins CnH2n+2 Single bonds only Straight or branched open chains

Alkenes Olefins CnH2n One double bond, remainder single

Straight or branched open chain

Alkynes Acetylenes CnH2n-2 One triple bond, remainder single

Straight or branched open chain

Cyclanes Cycloalkanes, Cycloparaffins, Naphthenes

C2H2n or (CH2)n

Single bonds only Closed rings

Aromatics Benzene family

CnH2n-6 Resonance hybrid bonds (Aromatic bonds)

Closed rings

Hydrocarbon Families

• Single carbon bond• Double bond• Triple bond

__________________________• Open chains: Alkanes, alkenes, and alkynes

are of open chain structure.• Ring structure: Cyclanes and aromatics are

of ring structure.

CC CC

CC

Alkanes, alkenes, and alkynes

• 1 – meth

• 2 – eth

• 3 – prop

• 4 – but

• 5 – pent

• 6 – hex

• 7 - hept

• 8 – oct

• 9 – non

• 10 – dec

• 11 – undec

• 12 – dodec

Propane; Propene; and Propyne

Aromatics or Benzene Derivatives

Benzene rings can combine to form polycyclic aromatics, and side chains may be substituted for hydrogen atoms.

©© UNEP 2006 UNEP 2006

Assessment of a BoilerAssessment of a Boiler

1. Boiler performance• Causes of poor boiler performance

-Poor combustion-Heat transfer surface fouling-Poor operation and maintenance-Deteriorating fuel and water quality

• Heat balance: identify heat losses

• Boiler efficiency: determine deviation from best efficiency

©© UNEP 2006 UNEP 2006


Heat BalanceAn energy flow diagram describes geographically how energy is transformed from fuel into useful energy, heat and losses

StochiometricExcess AirUn burnt

FUEL INPUT STEAM OUTPUT

Stack Gas

Ash and Un-burnt parts of Fuel in Ash

Blow Down

Convection & Radiation

©© UNEP 2006 UNEP 2006


Heat BalanceBalancing total energy entering a boiler against the energy that leaves the boiler in different forms

Heat in Steam

BOILER

Heat loss due to dry flue gas

Heat loss due to steam in fuel gas

Heat loss due to moisture in fuel

Heat loss due to unburnts in residue

Heat loss due to moisture in air

Heat loss due to radiation & other unaccounted loss

12.7 %

8.1 %

1.7 %

0.3 %

2.4 %

1.0 %

73.8 %

100.0 %

Fuel

73.8 %

©© UNEP 2006 UNEP 2006


Heat Balance

Goal: improve energy efficiency by reducing avoidable losses

Avoidable losses include:

- Stack gas losses (excess air, stack gas temperature)

- Losses by unburnt fuel

- Blow down losses

- Condensate losses

- Convection and radiation

©© UNEP 2006 UNEP 2006


Boiler EfficiencyThermal efficiency: % of (heat) energy input that is effectively useful in the generated steam

BOILER EFFICENCY CALCULATION

1) DIRECT METHOD: 2) INDIRECT METHOD:

The efficiency is the different between lossesand energy input

The energy gain of theworking fluid (water and steam) is compared with the energy content of the boiler fuel.

©© UNEP 2006 UNEP 2006


hg -the enthalpy of saturated steam in kcal/kg of steam

hf -the enthalpy of feed water in kcal/kg of water

Boiler Efficiency: Direct Method

Boiler efficiency () = Heat Input

Heat Outputx 100 Q x (hg – hf)

Q x GCVx 100=

Parameters to be monitored: - Quantity of steam generated per hour (Q) in kg/hr - Quantity of fuel used per hour (q) in kg/hr- The working pressure (in kg/cm2(g)) and superheat

temperature (oC), if any - The temperature of feed water (oC) - Type of fuel and gross calorific value of the fuel (GCV) in

kcal/kg of fuel

©© UNEP 2006 UNEP 2006


Efficiency of boiler () = 100 – (i+ii+iii+iv+v+vi+vii)

Boiler Efficiency: Indirect Method

Principle losses:i) Dry flue gas

ii) Evaporation of water formed due to H2 in fuel

iii) Evaporation of moisture in fuel

iv) Moisture present in combustion air

v) Unburnt fuel in fly ash

vi) Unburnt fuel in bottom ash

vii) Radiation and other unaccounted losses

POLLUTION LOAD FROM BOILER FUELS BASED THERMAL POWER PLANT

Pollutants Emissions (in tones/day)

CO2 424650

Particulate Matter

4374

SO2 3311

NOx 4966

Carbon dioxide attack in boilers • In boiler systems, corrosion

resulting from carbon dioxide is most often encountered in the condensate system. Because feed water deaeration normally removes carbon dioxide from the boiler feed water, the presence of the gas in condensate is typically due to carbonate and bicarbonate decomposition under boiler conditions. For an approximation is estimated that feed water with a total alkalinity of 100 mg/l as calcium carbonate could be expected to generate a carbon dioxide level of 79 mg/l in the steam (alkalinity multiplied by a factor 0.79). Such a high carbon dioxide level would create a very corrosive condensate.

• Carbon dioxide corrosion is frequently encountered in condensate systems and less commonly in water distribution systems

Carbon dioxide attack in boilers

• Carbon dioxide exists in aqueous solutions as free carbon dioxide and the combine forms of carbonate and bicarbonate ions. Corrosion is the principal effect of dissolved carbon dioxide. The gas will dissolve in water, producing corrosive carbonic acid:

• H2O + CO2 -------H2CO3 -----------H+ + HCO3-• The low pH resulting from this reaction also

enhances the corrosive effect of oxygen

CO2 Capture and Sequestration

CO2 Emission

Municipal10%

Others12%

Agriculture11%Transport

3%

Industry64%

Boiler pollutions

• A chemical facility has a 35 GJ/h boiler which burns natural gas. In September of the reporting year, the boiler was retrofitted with low-NOX burner technology. The facility does not have CEM or stack test data for the boiler. Natural gas consumption is metered, and data is available from gas bills.

NOX - origins and effects

• includes NO, NO2 (but not N2O)• main source is combustion:

N + O2 NOX

• the N comes from – nitrogen in air (thermal NOx) – nitrogen in fuel (fuel NOx)

• Effects – precursor to ground level ozone – precursor to secondary fine particulate: nitrates– acid rain

Emissions Quantification - CO

• A chemical facility has a 35 GJ/h boiler which burns natural gas. In September of the reporting year, the boiler was retrofitted with low-NOX burner technology. The facility has a CEM which monitors flow rate and CO concentration from the boiler.

CEM data for CO Emissions

PERIODStack Gas Flow Rate

Measured CO concentration

Calculated CO emission rate

(dscm/min) (ppmv, dry) (kg/hr)

1:00 310 20.2 0.4301:10 305 23.9 0.5011:20 295 19.9 0.4031:30 315 20.5 0.4441:40 308 19.5 0.4131:50 320 29.5 0.6492:00 303 26.3 0.548

Emission Sources - SO2

• combustion of S-containing fuels in external and internal combustion sources– natural gas may contain mercaptan to permit

detection of leaks– light and heavy fuel oils can contain significant

amounts of sulphur

• flare emissions• process releases

Other Problems• Steam Blanketing: Firetube boilers

are most often used for incinerator heat recovery for economic reasons. Carbon steel boiler tubes are commonly used, and the tube metal temperatures are kept sufficiently low by the very rapid rate of heat removal as water flashes to steam on the outer surface of the metal. As steam bubbles form they float upward away from the tube surface, allowing fresh water to reach the tube. Excessive steam production in one area can "blanket" the area with steam, impeding water entry and allowing tube metal to approach flue gas temperature, damaging the tube. A ceramic "ferrule" sleeve at the entrance to each tube will prevent steam blanketing in this area of high gas velocity. Installation of ferrules to eliminate steam blanketing is possible, as long as gas side pressure drop does not become excessive.

DEAERATOR CRACKING

• In numerous deaerators, cracks have developed at welds and heat-affected zones near the welds. The cracking most commonly occurs at the head-to-shell weld below the water level in the storage compartment. However, it may also occur above the water level and at longitudinal welds. Because cracks can develop to the point of equipment failure, they represent a potential safety hazard requiring periodic equipment inspection and, when warranted, repair or replacement. Wet fluorescent magnetic particle testing is recommended for identification of cracks.

ECONOMIZER TUBES • The most severe damage occurs at the economizer inlet and, when

present, at the tube weld seams. Where economizers are installed, effective deaerating heater operation is absolutely essential. The application of a fast-acting oxygen scavenger, such as catalyzed sodium sulfite, also helps protect this vital part of the boiler.

• While oxygen pitting is the most common form of waterside corrosion that causes economizer tube failures, caustic soda has occasionally accumulated under deposits and caused caustic gouging. Usually, this type of attack develops in an area of an economizer where steam generation is taking place beneath a deposit and free caustic soda is present in the feedwater. The best solution to this problem is improved treatment that will eliminate the deposition.

Superheater Tubes

• Superheater tube failures are caused by a number of conditions, both mechanical and chemical. In any instance of superheater tube failure, analysis of the deposits found is an important factor in solving the problem. Magnetic oxide deposits at the point of failure are a direct indication of oxidation of the tube metal. This oxidation occurs during overheating where metal temperatures exceed the design temperature and the steel enters into a direct reaction with the steam to form magnetic iron oxide with hydrogen release. When the deposits found in the area of failure are primarily iron oxide, it may be necessary to explore a number of operating conditions in order to determine the initial cause.

Examples of common failures due to mud in the heating circuit:

common heating water:

after fine- filtration:

crack

Cut through damaged cast-iron boiler

Boiler Maintenances• A well-planned maintenance program avoids unnecessary down

time or costly repairs. It also promotes safety and aids boiler code and local inspectors. An inspection schedule listing the procedures should be established. It is recommended that boiler room log or record be maintained, recording daily, weekly, monthly, and yearly maintenance activities. This provides a valuable guide and aids in obtaining boiler availability factor to determine shutdown frequency, economies, length of service, etc.

• Even though the boiler has electrical and mechanical devices that make it automatic or semi-automatic in operation, these devices require systematic and periodic maintenance. Any "automatic" features do not relieve the operator from responsibility, but rather free him from certain repetitive chores, providing him with time to devote to upkeep and maintenance.

Thank you for your Attention

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Boilers الغلايات