May 2011 Newsletter

CAS Newsletter May 2011


Volume #10, Newsletter #10 May-2011
Chipkin Automation Systems Inc.

IN THIS ISSUE

Boilers

A boiler is a self-sufficient combustion system which is mainly used for heating of water or other fluids. It generally consists of a closed metal container or a vessel in which the pressurized water is subjected to heat and then converted into steam or vapors. This conversion of liquid into gaseous state or vapors is known as evaporation process. This heated water or steam generated inside the boiler can then be used for variety of purposes like:

  • Home heating systems
  • Steam turbines
  • Oil refining
  • Paper drying etc.

In the boiler furnace, the chemical energy in the fuel is converted into heat, and it is the function of the boiler to transfer this heat to the contained water in the most efficient manner.

The flow of a typical boiler plant arrangement is shown in the figure below.

A good boiler system design should be such that:

  • It produces superior class steam for use in plants and industrial applications.
  • It results in maximum absorption of heat energy produced by the combustion reaction.

There are three means by which heat can be transferred to the water inside the boiler, i.e. via radiation process, conduction process and convection process. The relative percentage of each is dependent upon the type of boiler, the designed heat transfer surface and the fuels.

The heating surface of a boiler can be defined as the section of boiler which tends to contain hot combustion or flue gases at its one end and liquid on the other. In other words, any metallic component of the boiler which helps in steam generation would be regarded as its heating surface.

Major Parts

A boiler normally consists of following four major sections:

  1. Burner: This part of the boiler is responsible for commencing the combustion process inside the boiler. It receives electronic signals from the temperature sensing devices like thermostats, as and when the heat needs to be generated out of the system. In most cases, a fuel tank is positioned just next to the boiler for providing fuel source. A filter system is employed to pump the fuel to the boiler. This fuel is then sprayed as fine particles via a nozzle mounted on the burner which tends to produce ignition and combustion reaction inside the chamber.
  2. Combustion Chamber: The burning of the fuel takes place inside a combustion chamber which is generally constructed of cast iron material. This combustion chamber is designed to experience intense heat energy since the temperature inside the chamber tends to reach very higher limits in a very short period of time. Heat produced inside this chamber is then finally transmitted to the heat exchanger unit.
  3. Heat Exchanger: A sequence of flue passages is used to filter the liquid inside the combustion chamber in a boiler arrangement. “The pressurized, boiling water is then pumped through pipes to baseboard heaters or radiators, which give off the heat energy produced in the boiler.”[4]
  4. Fuel Sources: For its functioning, a boiler consumes variety of fuels such as heating oil, kerosene oil, liquid propane etc.

Main Features

Key features of boilers include:

  • The efficiency offered by a typical boiler system falls between 75% and 85%. However, advanced boiler systems made up of copper heat exchangers have now been designed which are capable of providing as high as 90% efficiency.
  • Besides heating applications, a usual boiler system can be employed in many other areas like steam-operated locomotives, external combustion engines and power generation plants.
  • In order to get high efficiency out of boiler systems, they must be periodically cleaned and maintained. The maintenance process generally includes activities like making combustion chamber free from useless remains and debris, changing of components such as gaskets and checking of temperature.
  • The installation and maintenance of boiler systems must be carried out by professionally skilled and certified personnel. Inappropriate installation and operation of boilers can result in very hazardous effects owing to the severe heat energy involved with them.
  • The efficiency of a boiler system also depends upon the total heating surface encompassed by the boiler. More the heating surface more is the efficiency. The heating surface of a boiler is generally represented in square feet.
  • As a general rule, horse power rating is used for small boilers and thousands of pounds of steam rating is used for large boilers in industrial applications.

Types of Boilers

In general, there are two major types of boilers available for industrial use:

  1. Fire Tube Boilers: In this design, the boiler tubes are surrounded by the liquid which needs to be heated whereas the hot gases produced out of combustion reaction are passed via these boiler tubes.
  2. Water Tube Boilers: Their design is just opposite to fire tube boilers design. Here, the hot combustion gases are circulated around the boiler tubes whereas the tubes enclose the water to be heated.

Boiler Control

Boilers are the primary source of steam and hot water generation in industrial processing plants where steam demands vary very frequently according to the requirements. Hence, a well designed boiler must be capable of giving immediate response to these load demand variations. While doing so it must also maintain its efficiency and safety features. In order to achieve this, various techniques of boiler control are available. Some of these are meant as local boiler controls whereas the more advanced ones are said to be direct digital controls i.e. DDC.

Local boiler controls are generally employed for boiler systems functioning in stand alone manner. It is very necessary to set right water levels in the systems such as dry fired boilers owing to the risk involved with their operation.

On the other hand the direct digital controls are mainly applied in situations where multiple boilers are used. DDC controls are individual systems which are capable of handling multi- boiler staging as per demand changes. Moreover, they can control hot water multi-pump functional sequencing as well as home hot water services. Also, they help in collecting and analyzing surplus amount of boiler data. In addition to all, they are provided with an exclusive hot water reset schedule feature which results in smaller cycle rates than exterior temperature of air. These control techniques offer high adaptability and reduced running costs in boiler plant management.

In domestic applications a special device named aquastat is employed for boiler control whereas in commercial boiler applications involving large horsepower boilers far advanced control systems are used. While selecting a boiler control type for a particular application, one must consult experienced control manufacturers and engineers.

Types of Boiler Controls

Based upon the system specifications and user requisites, local boiler controls are directly manufactured inside the factories and made available outside as complete systems. Following are the major controls available for boilers:

  1. Multi-boiler Staging: In this method, multiple boilers are staged on and off depending upon the load demand. Primarily, a number of cast iron boilers are applied for this selection. Either electro-mechanical control or solid-state control is put into use for this kind of boiler control technique.
  2. Modulating Control: In this method, the quantity of fuel and air supplied to the burner varies according to the load demand. It ranges its boiler firing rate from low fire to high fire and everything in between based on specific input temperatures that determine demand such as delta T. In this technique, the steam pressure and hot-water temperature gets measured depending upon which a nonstop control signal is generated. This signal usually serves as an indication for the fuel which needs to be supplied to the burner for combustion. Whenever, there is drop in pressure or temperature, the firing rate increases accordingly. This technique results in better boiler efficiency.
  3. On – Off Control: In this method, the boiler gets on and reaches upto high fire level and then settles at that stage until a pre-determined set point is attained.
  4. Step-up/Step-down: In this method of boiler control, more than two firing rates exist depending upon the heating demand. Here, the firing rates generally vary from low to low, high or medium fire.
  5. Oxygen Trim Control: In this technique, the quantity of oxygen present in the combustion gases is determined and then the available surplus air is cut down to achieve high burning efficiency. This method of boiler control enables sound control of emission as well as excess air. It also results in simple override of carbon monoxide or opacity.
  6. Excess Air Regulation Control: In this method, a perfect ratio of excess air to fuel supplied is maintained to achieve high burning efficiency as well as reduced heat loss. In general, gas, oil and coal powered boilers do not have the capability to provide a perfect blend of fuel and air. Hence, in these circumstances, the use of this method becomes absolutely essential. Effective implementation of this technique will result in better heat-transfer rates, pre-warning of combustion related issues and considerable fuel savings.
  7. Air/Fuel Cross Limiting Control: In this technique of boiler control, the air supply is increased prior to an increase in fuel supply as well as the fuel supply is decreased before the air supply happens to drop in the system. Due to this, the safety of the boiler system will always be maintained along with optimized fuel consumption. This cross-limiting combustion-control strategy hence proves to very effective in reducing the danger of explosion due to improper air to fuel ratio in the system. The execution of this method will make the system capable of adapting to quick changes occurring in fuel and air flows. Also, it helps in better fulfillment of steam demand.
  8. Drum Level Control: This method is often applied for boiler systems in which the drum water level is considered to be significant. If the level of water happens to be very low then it will result in exposure of boiler tubes to the heat and atmosphere which in turn leads to overheating and destruction of these tubes. On the other hand if the level of water happens to be exceedingly high, then it will create problem in separation of moisture from steam ultimately leading to reduced boiler efficiency and transport of undesirable moisture to the process or turbine. Hence, an appropriate level of water must always be maintained in a boiler drum. This level control is always done at constant steam load demand. Three types of drum-level control designs mainly exist for boiler applications which include single-element drum-level control, two-element drum-level control and three-element drum-level control.

Single-element Drum-level Control

This is a very simple kind of drum level control design. It needs single analog input for its operation and in return provides single analog output. Hence, it is named single element control. Because there’s no relationship between drum level and steam or feedwater flow, it can be applied only to a single feed pump on a single boiler supplying a relatively stable load. Its performance is not as effective as compared to other two level control designs. A typical drum level control with single element module is shown in the figure below.

Two- element Drum-level Control

This drum level control design is particularly suitable in case of single drum boilers where the feedwater is available at a constant pressure. Two-element control includes the same level element used for the single-element configuration but has an added steam-flow element that provides a density-corrected mass flow-rate signal to control the feedwater flow. In this design, presence of double control elements tends to provide rigid drum level control. A typical drum level control with two element module is illustrated in the figure below.

Three-element Drum-level Control

Three-element drum-level control is suited for handling variable feedwater pressure or multiple boilers with multiple feedwater pumps. In this design, three elements are used, each for controlling level, steam and feedwater flow respectively. This system offers far better and advanced drum level control as compared to all other systems. For best control, correct flow values of both steam as well as feedwater must be maintained with regard to density. A typical drum level control with three element module is shown in the figure below.


Boiler Efficiency

Boiler Efficiency is a term which establishes a relationship between energy supplied to the boiler and energy output received from the boiler. It is usually expressed in percentage. As a general rule,
Boiler efficiency (%) = heat exported by the fluid (water, steam) / heat provided by the fuel x 100.

Types of Boiler Efficiency

The efficiency of a boiler may be classified into following three major types:

  1. Combustion Efficiency
  2. Thermal Efficiency
  3. Fuel-to-Steam Efficiency

Amongst all the three above mentioned boiler efficiencies, the fuel-to-steam efficiency is considered to give the most accurate representation of boiler efficiency on the whole. This is due to the fact that fuel-to-steam efficiency takes into account, the radiation and convection losses while performing efficiency calculations. Typically, it is the job of the boiler manufacturer to define boiler efficiency so that any type of economic analysis could be done properly.

Combustion Efficiency

Combustion efficiency generally gives an idea about the fuel burning capability of a burner. This type of efficiency is determined by the quantity of fuel which is left unburned in the boiler along with the surplus exhaust air. For getting high boiler efficiency, their burners should be well designed to provide low quantities of unburned fuel and excess air.

Combustion efficiency tends to vary with the types of fuel sources. In general, gaseous and liquid fuels result in very small amount of unburned fuel as well as 15% surplus air levels; hence they offer highly efficient burning as compared to solid substances. By operating at only 15% excess air, less heat from the combustion process is being used to heat excess air, which increases the available heat for the load.

Thermal Efficiency

This type of boiler efficiency is only used to assess the performance of heat exchanger units used in boilers. It basically determines the efficacy via which a heat exchanger would convey heat generated by burning process to the fluid in the boiler. While doing so, it does not take into account the radiation and convection losses occurring in the boiler sections. Hence, thermal efficiency is not considered valuable for economic analysis since it doesn’t reflect correct fuel consumption of a boiler system.

Fuel-To-Steam Efficiency

Fuel-to-steam efficiency is helpful in determining the overall efficiency of a boiler since it takes into consideration both the thermal efficiency i.e. heat exchanger effectiveness and the radiation and convection losses. This is the type of boiler efficiency which is ought to be used for making all types of economic assessments.

Methods of Determination

The two major methods employed to find out the fuel-to-steam efficiency of a boiler are explained below:

Input-Output Method

This method of efficiency determination largely depends upon the input-output ratio determination of the boiler. In this method, the output of the boiler derived in BTUs is divided by the boiler input supplied in BTUs and then the resulting number is multiplied by 100.

Heat Loss Method

It is also referred to as heat balance efficiency measurement method. This method of efficiency determination takes into account all kinds of heat losses occurring inside the boiler. The true boiler efficiency is calculated by summing up the percentage of all stack, radiation and convection losses and then finally deducting the resultant sum from 100 percent. This entire calculation will provide actual fuel-to-steam boiler efficiency.

Types of losses

Two major types of losses which take place inside a boiler system are mentioned below:

Stack Losses

The stack temperature is the temperature of the combustion gases (dry and water vapor) leaving the boiler and reflects the energy that did not transfer from the fuel to the steam or hot water. In other words, it gives an indication about the quantity of heat energy lost due to dry exhaust gases and moisture loss. It is found valuable in determining the true efficiency of a boiler. A lower value of the stack temperature is always preferred for gaining well efficient heat exchanger performance and greater fuel-to-steam boiler efficiency.

Radiation and Convection Losses

Radiation losses are defined as the losses which occur due to radiation i.e. emission of heat energy out of the boiler whereas convection losses are the losses happening due to the air circulating around the boiler. Nearly all kinds of boilers experience these two significant losses. Radiation and convection losses, expressed in Btu/hr, are essentially constant throughout the firing range of a particular boiler, but vary between different boiler types, sizes, and operating pressures.

Boiler Design Criteria

To achieve high efficiency out of a boiler system, it must be designed in such a way that it meets all the required design criteria which mainly includes:

  1. Required number of boiler passes
  2. Suitability of boiler and burner
  3. Availability of fuel control within the boiler system
  4. Adequate heating surface of the boiler
  5. Well designed pressure vessel

Factors Affecting Boiler Efficiency

Some of the important boiler-efficiency deciding factors are explained in brief below:

Stack Temperature

It is also referred to as flue gas temperature. It is defined as the temperature level at which the hot exhaust gases make their way out of the boiler. The flue gas temperature must be a proven value for the efficiency calculation to be reflective of the true fuel usage of the boiler. Lower than real stack temperature values must always be used for boiler efficiency calculations.

Fuel Specification

The specification of a fuel source can immensely affect the efficiency of a boiler system. For example, if the hydrogen content within a gaseous fuel source is comparatively high, extra water vapors get generated in the burning process. These water vapors tend to consume heat energy from the boiler for shifting their physical state during combustion. The efficiency of the boiler generally drops if huge loss of water vapors takes place. Due to this, the fuel oil offers greater boiler efficiency as compared to natural gas. To get an accurate efficiency calculation, a fuel specification that represents the jobsite fuel to be fired must be used.

Excess Air

Excess air is defined as the amount of surplus air provided to the burner which is more than the necessary air needed to carry out combustion process. This given excess air mainly acts as a safety air reservoir for combustion in difficult situations such as inadequate air conditions.

However, at the same time, this more than required air tends to consume heat energy produced by combustion which in turn affects the heating efficiency of the boiler. Seasonal changes in temperature and barometric pressure can cause the excess air in a boiler to fluctuate 5% – 10%. A realistic excess air level for a boiler in operation is 15% if an appropriate safety factor is to be maintained.

Ambient Temperature

The efficiency of a boiler also depends upon the ambient air temperature surrounding the boiler. For every 40 degree shift in ambient temperature, the efficiency of a boiler can get affected by at least 1%. Since all the boiler rooms are maintained at moderately warm temperature, majority of the efficiency computations takes upon 80 deg. F as the ambient temperature value.

Radiation & Convection Losses

These are the losses which emerge due to radiation of heat energy from the boiler. To eliminate the effect of these losses, boiler systems are usually shielded with some sort of insulation material. The presence of these losses extremely influences the efficiency of a boiler. In cases where these losses are not taken into consideration while performing efficiency calculations, accurate fuel consumption value can never be attained.

A boiler must always be designed in such a way that the radiation and convection losses get minimized. These losses tend to increase in proportion to the wind or air velocity prevailing around the boiler. Hence, the boiler systems located in open atmosphere experience more radiation and convection losses as compared to room boilers.


Boiler Fuels

All boiler systems employ a fuel mechanism which basically comprises of the apparatus needed to supply fuel for heat generation. The design of the apparatus in use varies according to the kind of fuel employed in the system. Variety of fuels is available for application in boilers, each having different chemical properties. Major chemical characteristics of boiler fuels include:

  • C/H2 ratio: It is a unique ratio which mainly determines the quantity of supply air needed for absolute combustion of a particular fuel source. More is the value of carbon in the fuel; excess supply air would be needed for carrying out whole burning process.
  • Calorific value: The calorific value is the quantity of heat obtained per kilogram for solid or liquid fuel or per m3 for gaseous fuel when burnt with an excess of oxygen in a calorimeter. By carrying out a calorific value test, one can distinguish between high and low calorific value fuels. In general, the combustion reaction products containing H2O in the form of liquid indicate Higher Calorific value whereas H2O in vapor form indicate Lower Calorific value.

Their energy measurement unit is either BTUs i.e. British Thermal Units or KWs i.e. Kilowatts. One can convert between the two units by means of conversion factor i.e. 3.46 BTU/W.

Each and every fuel whether it is in solid, liquid or gaseous form is explosive and can prove hazardous if not used according to the recommended safety guidelines. When monitoring the efficiency of a combustion process, it is important to know the fuel being burned since this information will help not only determine a boiler’s optimal working conditions but also maximize the boiler’s efficiency.

Commonly Used Fuels

The list of major fuels which are employed in boiler systems is given below:

  1. Natural Gas
  2. Propane
  3. Oil
  4. Electricity
  5. Solids Fuels like Coal & Wood
  6. Renewable Energy

Electricity

Electricity is an alternative source to gaseous fuels employed in traditional boiling systems. It tends to give a heating value around 3.4kBTU per kWh. Use of electricity in boiler systems offers various advantages which are mentioned below:

  • Usage of electricity as boiler fuel results in extremely compact design and light weight boiler systems which can be operated at comparatively less cost.
  • Besides, it results in entirely noise free boiler operation.
  • It can be easily employed in various kinds of heating and cooling devices, for example, basic resistance heating systems, air conditioning systems and heat pumps etc.

LPG (Liquid Petroleum Gas)

In practice, LPG is mainly used in applications where the availability of natural gas is either very limited or costly. LPG works as a boiler fuel in similar manner as natural gas. However, the boiler in use must be capable of conversion features so that it could be made compatible with LPG.

Solid Fuels

Major solid fuels used for burning in a boiler include coal and wood. They were the only fuel sources available for use in boiler systems prior to the emergence of heating fuel oil. These are the cheapest means of boiler fuels which are getting exhausted day by day due to uncontrolled use. However, boiler systems employing coal or wood as fuel source call for some extra precautions and care due to the reasons mentioned below:

  1. The use of solid fuels results in more dust and ashes as compared to heating oil and natural gas.
  2. Since the amount of carbon content present in coal is very high, it produces a substantial amount of carbon dioxide gas upon burning.
  3. Also, presence of high carbon value needs extra oxygen for combustion because of which relatively high amount of combustion air would be required for burning of coal as compared to other boiler fuels.
  4. Moreover, burning of coal inside a boiler results in emission of polluted ingredients such as NOx, sulfur dioxide i.e. SO2, sulfur trioxide i.e. SO3 etc. Typically, a chemical reaction takes place between emitted sulfur dioxide and water vapor present in the atmosphere due to which a feeble type of sulfuric acid is created that happens to be one of the major reasons for acid rain.

Different forms of coal are available for burning process, most common among them are listed below:

  1. Anthracite
  2. Bituminous
  3. Sub-bituminous
  4. Lignite

Oil

With the advent of fuel oil, solid fuels such as coal and wood increasingly got replaced in nearly all parts of the world owing to its cleaner and ash free combustion process. Oil fuels generally consist of less carbon content as compared to solid fuels such as coal, which in turn results in less emission of carbon dioxide upon combustion. On the other hand, oils contain higher carbon content as compared to natural gas producing high amounts of carbon dioxide due to burning.

The fuel oil employed for boiler use is mainly manufactured from a mix of extremely heavy hydrocarbons, which tend to contain relatively high amounts of hydrogen content in comparison to coal. Burning of a fuel oil usually produces same kind of pollutants as produced with burning coal. Heating oil is a boiler fuel which is widely employed in the northeastern areas of the United States whereas in other parts of the world, it is facing severe competition with the gaseous boiler fuels available.

Diversity of oil fuels is available for heating such as oil #2, oil # 4, and oil # 6. Fuel oil #2 is popularly referred to as the home heating fuel. It is almost identical to the diesel oil fuel which is largely employed in vehicles and automobiles. Its energy value is found to be approximately 139 kBTU per gallon.

Boiler and heating systems that employ oil for its operation happen to be more expensive than gas powered boiler systems since they need complicated burner mechanism as compared to their gas counterparts for efficient firing. However, at the same time, this difficulty of ignition (or firing) in case of heating fuel turns out to be a great plus point since it results in safer storage of fuel oil in comparison to gas. Otherwise, a leakage in the fuel tank could prove to be very costly and hazardous.

Natural Gas

Natural gas is the key fuel source for boilers which is widely employed in United States and Europe for home heating needs. It is largely prepared from methane along with a mixture of few other gases in small proportions. Natural gas has an energy content of about 100kBTU per therm or 103kBTU per ccf (100 cubic feet). However, anecdotal evidence suggests that the actual heating value of “Natural Gas” coming out of the distribution pipe may vary from as little as 60kBTU up to 160kBTU per ccf.

Natural gas can be conveniently put into use for boiler applications since it can be transported easily via gas pipelines when in gaseous sate and trucks or ships when in liquid state. Very less amount of air is needed for burning of natural gas owing to its unique C/H2 ratio. This fuel contains quite low values of carbon and high values of hydrogen because of which the combustion of natural gas results in production of less greenhouse gases which are considered to be highly responsible for global warming. Also, the burning of natural gas is found to be very clean as compared to the burning of oil and solid fuels oil.

In general, an equivalent amount of natural gas burns to generate approximately 30% and 45% less carbon dioxide than heating oil and coal respectively. Besides, carbon dioxide gas, burning of natural gas emits an ingredient called NOx whereas the quantity of sulfur dioxide i.e. SO2 and other emission particles is almost insignificant. However, if the burning of gas takes place facing scarcity of combustion air, there is a possibility of volatile hydrocarbons generation which is very unsafe to human health and surroundings. Hence, care must be exercised to avoid these hazardous possibilities.

Nowadays, natural gas fuel reserves are getting exhausted at a rapid rate. Hence, substitutes for this boiler fuel need to be discovered very soon.

Propane

Propane is a boiler fuel which is basically manufactured out of refining process carried out for petroleum goods. It is generally carried and delivered to the usage point with the help of pressurized gas containers. Unlike natural gas, the energy content of propane is measured in gallons instead of cubic feet. It usually consists of 91 kBTU per gallon. In general, propane is available at a fairly higher price as compared to natural gas. Just like natural gas, it offers simple and economic integration into the forced-air heating systems, predominantly in the US market.

Renewable Energy Sources

Variety of renewable energy sources is available for use as boiler fuels. Most common of them includes solar energy and wind energy. The energy from solar radiations can be utilized in many devices such as solar water heating systems and solar cell systems whereas wind energy can be easily used in wind generators. This category of fuel resources proves to be extremely useful for people residing in distant areas where other fuel sources are difficult or costly to achieve. Hence, places which get abundant supply of sun heat are the justified locations for usage of solar energy. Moreover, photovoltaic systems operating via solar energy can be used for production of electricity to meet the power requirements in these areas.

Other Fuels

Some other fuels commonly used for consumption in boilers are listed below:

  1. Diesel oil
  2. Gasoline
  3. Butane
  4. Bio fuels like ethanol

All these fuels have unique combustion characteristics which tend to influence the performance efficiency and emissions of the burning process.


Boiler Water Source

Both hydronic boilers as well as steam boilers require a water source for their operation. This boiler feed water can be obtained either in the form of city water supply or well water that is provided by the pump. Barring any leaks, drips, or weeping in your system, the supply from the well or city is necessary to keep the water level at desired levels.

A boiler fired in its dry state may lead to hazardous results. Hence, it is very crucial to maintain appropriate water levels in a boiler system. In case of hydronic boilers, the system must be entirely filled with water whereas in steam boilers, the level of water should not touch the mains otherwise the system will not work properly. In steam boilers, a control at the water supply must always be maintained to limit the water levels.

A gate or ball valve is usually employed to stop the supply of water in periods of maintenance or water leaks. When the water supply is put to a halt, the power and fuel source supply should also be cut from the boiler system. After the shut off valve there should be a back flow preventer, however there may be some older systems that do not have back flow preventer’s. Current local and national codes require back flow preventer’s to keep the supply water from being contaminated by back flow water from the hot water loop. Subsequent to the back flow preventer, a pressure reduction valve should always be mounted for the purpose of bringing down the supply water pressure upto 12 P.S.I. After the pressure reducer, the source supply water should be fed into the return or supply loop depending on the application and type of system.

Water Treatment

The boiler feed water must undergo various treatment and conditioning processes before entering the boiler system due to following major reasons:

  • Water treatment helps in maintaining continuous heat exchange within the system.
  • It provides resistance against corrosion.
  • It helps in generation of high grade steam output.

Two major ways via which the boiler water supply can be purified include: External water treatment & Internal water treatment methods.

External Water Treatment

In this method, the boiler feed water is treated and purified outside the boiler system. This method of water treatment is normally chosen when the levels of impurities present in feedwater reaches so high that they can damage the inside structure of the boiler system in use. Hence, the impurities must be removed from feed water before water enters inside the boiler via external method.
Various kinds of external water treatment techniques are available such as water softening, evaporation process, deaeration technique and membrane contractors etc. Any of these techniques can be utilized depending upon the requirements of a specific boiler system.

Internal Water Treatment

In this method, the treatment & conditioning of water impurities is carried out inside the boiler only. The necessary reactions tend to take place either in the water feed lines or exactly in the boiler. This method of water treatment can be employed either alone or in combination with external water purification techniques. Internal water treatment method basically fights with following feed water problems:

  1. Water hardness
  2. Sludge formation
  3. Oxygen feed
  4. Water foaming etc.

Engineering Units – Horsepower (Boiler)

An engineering unit falls under Power group, commonly used by automation professionals.

  1. The boiler horsepower is defined to be the power required to convert 30 pounds (13.61 kilograms) per hour of water at 100 °F (37.78 °C) to saturated steam at a pressure of 70 pounds per square inch gauge (482.6 kilopascals gauge).
  2. A unit of power, 19th-20th centuries, defined by the Boiler Code Test Committee of the American Society of Mechanical Engineers, and used in rating a boiler’s capacity to deliver steam to a steam engine. One boiler horsepower is about 33,478.8 Btu per hour (about 9,809.5 watts).
  3. This unit is commonly used in the US unit system. Horsepower (boiler) (HP) has a dimension of ML2T-3 where M is mass, L is length, and T is time.

Conversion to SI and other common units

1 Horsepower (boiler) equals to:

Other Common Units
98094995193.34523 Abwatt (emu of power)
33471.3856899 Btu (IT) per hour
557.8564282 Btu (IT) per minute
9.2976104 Btu (IT) per second
33493.8494438 Btu (therm.) per hour
558.2301701 Btu (therm.) per minute
9.3038394 Btu (therm.) per second
8434776.6376959 Calorie (IT) per hour
140579.9376116 Calorie (IT) per minute
2342.9891507 Calorie (IT) per second
8440269.9574268 Calorie (therm.) per hour
140671.1659571 Calorie (therm.) per minute
2344.5292421 Calorie (therm.) per second
13.3371917 Cheval-vapeur (horsepower)
98094995193.34523 Dyne-centimeter per second
98094995193.34523 Erg per second
26046379.3137274 Foot-pound force per hour
434106.6488788 Foot-pound force per minute
7235.1140845 Foot-pound force per second
232783.3473936 Foot-poundal per second
13.154735 Horsepower (550 ft-lbf/s)
13.154735 Horsepower (British)
13.3371917 Horsepower (cheval-vapeur)
13.3371917 Horsepower (metric)
13.1487513 Horsepower (water)
1000.294285 Kilogram force-metre/second
100.0294285 Prony
2.5007063 Ton (refrigeration, UK)
2.7893214 Ton (refrigeration, US)
9809.4995193 Volt-ampere
9809.4995193 Watt
9807.6357144 Watt (int. mean)
9807.8809519 Watt (int. US)

Communication Protocol Support

This engineering unit is supported by the following communication protocols:

1. CIP (includes Ethernet/IP)

  • Enumeration=0x260A
  • Base Unit=9.8095 • 10 3 • W

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