Brushed dc motor

The brushed dc motor is all around us. From small gadgets to heavy machinery, these motors continue to play a vital role in daily life. Understanding how they work, their benefits, and their downsides can help you make informed decisions for your projects.

Introduction: The Enduring Legacy of Brushed DC Motors

Brushed DC motors is widely used in various applications, thanks to their simple design and easy control. Their history dates back over a century, evolving from basic mechanical units to powerful machines used today.

  • Advantages:
  • Simple construction
  • Affordable
  • Easy speed control
  • Limitations:
  • Lower efficiency
  • Higher maintenance needs
  • Shorter lifespan compared to brushless motors

Understanding Brushed DC Motor Operation: A Deep Dive

Brushed DC motors are based on fundamental principles of electromagnetism. When electricity flows through a coil inside the motor, it creates a magnetic field. This field interacts with permanent magnets, causing the rotor to spin.

The Role of the Commutator and Brushes

The commutator and brushes work together to maintain the motor’s rotation. The brushes provide a connection between the power source and the rotating commutator. As the commutator spins, it reverses the direction of the current, allowing continuous motion.

Voltage, Current, and Motor Speed

More voltage increases the speed of the motor. Higher current generally leads to more torque. Keep in mind that increasing both voltage and current can lead to overheating if not managed properly.

Types and Specifications of Brushed DC Motor

Brushed DC motors can be categorized by size, power, and specific applications. Here’s a closer look:

Key Specifications

  • Torque: Measures how much force the motor can apply.
  • Speed: Typically expressed in RPM (revolutions per minute).
  • Efficiency: Ratio of useful power output to input.
  • Operating Voltage: Range where the motor functions best.

Examples of Brushed DC Motors

  • Miniature Motors: Used in toys and small devices.
  • Standard Motors: Common in handheld tools and appliances.
  • High-Power Motors: Applied in industrial settings for tasks requiring more torque.

Advantages and Disadvantages of Brushed DC Motor: A Balanced Perspective

Brushed DC motors come with notable benefits and some drawbacks.

Advantages

  • Simplicity: Less complex than other types of motors.
  • Affordability: Lower cost makes them attractive for many applications.
  • Control: Easy to adjust speed and direction.

Disadvantages of Brushed DC motor

  • Efficiency: Generally less efficient than brushless alternatives. Studies show they can be around 70-80% efficient, while brushless motors can reach 90-95%.
  • Maintenance: Brushes wear out over time and require replacement.
  • Lifespan: Typically shorter than brushless motors, affecting long-term use.

Applications of Brushed DC Motors Across Industries

Brushed DC motors find their place in numerous everyday items and specialized machinery.

Everyday Appliances

These motors are commonly found in:

  • Toys: Driving mechanisms in remote-controlled cars.
  • Hand Tools: Powering drills and other handheld devices.

Industrial Uses

In industries, brushed DC motors are critical for:

  • Small-Scale Automation: Operate conveyor belts and robotic arms.
  • Electric Vehicles: Used in various automotive applications.

Selecting and Maintaining Brushed DC Motors: Practical Tips and Best Practices

Choosing the right brushed DC motor is essential for optimal performance.

Step-by-Step Guide for Selection

  1. Identify Your Needs: What will the motor power?
  2. Check Specifications: Look for torque, speed, and voltage requirements.
  3. Consider Size: Ensure it fits your application without overcrowding.

Installation, Operation, and Maintenance Tips

  • Installation: Follow guidelines to avoid damaging the motor.
  • Operation: Monitor temperature to prevent overheating.
  • Maintenance: Regularly inspect brushes and replace them when necessary.

Troubleshooting Common Issues

  • Overheating: Check for excessive current draw.
  • Noise: Inspect brushes for wear and tear.

Conclusion: The Continued Relevance of Brushed DC Motors

Brushed DC motors remain relevant due to their simplicity and effectiveness in various applications. While they have disadvantages, such as lower efficiency and higher maintenance needs, they are still a viable choice for many uses. As technology evolves, it will be interesting to see how brushed DC motors adapt and continue to serve crucial roles in different sectors.

Embrace the versatility and affordability of brushed DC motors for your next project, ensuring you make the most of their capabilities

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Brushless DC Motor

The rise of the brushless DC motor (BLDC) is hard to miss. These motors are everywhere, from the devices we use daily to the advanced technologies powering our vehicles. Their swift adoption marks a shift in how we approach motor technology. BLDC motors offer various advantages over traditional brushed DC motors, including improved efficiency and reduced maintenance. This article will explore everything you need to know about BLDC motors, highlighting their workings, types, pros and cons, applications, and maintenance tips.

How Brushless DC Motors Work:

A Deep Dive into the Technology

Brushless DC motors operate on simple principles that make them efficient. Unlike brushed motors, they use electronic commutation instead of mechanical brushes. This design translates into less friction and wear. Here are the key components that make BLDC motors tick:

Key Components:

  • Stator: The stationary part containing coils of wire that create a magnetic field.
  • Rotor: The rotating component that interacts with the stator’s magnetic field.
  • Controller: The vital component that manages the power supply to the motor, ensuring the rotor spins smoothly.

In essence, the controller sends signals to the motor, telling it when to turn, creating a seamless motion. For a better understanding, check out this illustrative diagram that shows how these components interact.

Types of Brushless DC Motors: Exploring the Variations

When it comes to BLDC motors, variety is essential. Here are the main types:

Permanent Magnet vs. Electronically Commutated Motors

  • Permanent Magnet Motors: Use magnets in the rotor for strong magnetic fields.
  • Electronically Commutated Motors: Rely on electronic circuits to switch current flow, enhancing performance.

In-runner vs. Out-runner Configurations

  • In-runner Motors: Have the rotor inside the stator, making them compact and efficient.
  • Out-runner Motors: Feature the rotor outside, often providing higher torque for lower RPMs.

Motor Winding Types

Different winding configurations affect a motor’s behavior:

  • Star (Y) Winding: Good for low voltage and current.
  • Delta (Δ) Winding: Offers more power, usually at higher voltages.

Advantages and Disadvantages of Brushless DC Motors

Understanding the pros and cons is crucial for making an informed decision about BLDC motors.

Advantages:

  • High Efficiency: BLDC motors can achieve efficiencies of up to 90%, significantly reducing operational costs compared to brushed motors, which can be as low as 60%.
  • Longer Lifespan: With no brushes to wear down, these motors can last years longer with minimal maintenance. For example, companies report using BLDC motors for over 10,000 hours versus just 1,500 hours for brushed motors.

Disadvantages:

  • Higher Initial Cost: The advanced technology comes with a price. BLDC motors typically cost 20-30% more upfront.
  • Complexity: They require more sophisticated control systems, which can be daunting for some applications.

Applications of Brushless Motors Across Industries

Brushless DC motors play a vital role in various sectors, showcasing their versatility.

Electric Vehicles and Hybrid Powertrains

BLDC motors are essential in electric vehicles. They provide high efficiency, allowing vehicles to travel further on a single charge. In fact, around 50% of electric vehicles use BLDC technology.

Robotics, Drones, and Industrial Automation

These motors enhance precision and performance in robotics and drones. For instance, many drones utilize BLDC motors for improved speed and maneuverability, proving essential for aerial tasks.

Consumer Electronics and Household Appliances

From vacuum cleaners to computer fans, BLDC motors are found in a plethora of household devices due to their low noise and energy-saving features.

Selecting and Maintaining Your Brushless DC Motor: A Practical Guide

Choosing and taking care of a BLDC motor is vital. Here’s how:

Selection Factors:

  • Application needs: Determine speed, torque, and size requirements.
  • Control System: Ensure it aligns with your motor type.

Installation and Operation Tips:

  • Follow manufacturer guidelines closely to avoid damage.
  • Ensure proper alignment during installation for optimal performance.

Maintenance Guidance:

  • Regularly check connections and settings.
  • Address common issues like overheating or abnormal noises promptly.

Conclusion: Embracing the Efficiency and Power of BLDC Motors

In summary, brushless DC motors provide numerous benefits such as high efficiency, longevity, and diverse applications across several industries. Future advancements promise to enhance their capabilities even further, making them a staple in modern technology. Explore the suitable applications and resources to integrate BLDC motors effectively into your projects for maximum benefit.

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Energy audit

The facility inspection for energy Audit

The Facility Inspection:

Once all of the basic data has been collected and analyzed, the energy audit team should tour the entire facility to examine the operational patterns and equipment usage, and should collect detailed data on the facility itself as well as on all energy using equipment. This facility inspection should systematically examine the nine major systems within a facility for using portable instrumentation and common sense guided by an anticipation of what can go wrong. These systems are: the building envelope; the boiler and steam distribution system; the heating, ventilating, and air conditioning system; the electrical supply system; the lighting system, including all lights, windows, and adjacent surfaces; the hot water distribution system; the compressed air distribution system; the motors; and the manufacturing system. Together, these systems account for all the energy used in any facility; examining all of them is a necessary step toward understanding and managing energy utilization within the facility.ae for Energy audit.

  1. 1. Introductory Meeting

The audit leader should start the audit by meeting with the facility manager and the maintenance supervisor. He should briefly explain the purpose of the audit and indicate the kind of information the team needs to obtain during the facility tour. If possible, a facility employee who is in a position to authorize expenditures or make operating policy decisions should be at this initial meeting.

  1. Audit Interviews

The auditor must also interview the floor supervisors and equipment operators to understand the building and process problems. Line or area supervisors usually have the best information on the times their equipment is used. The maintenance supervisor is often the primary person to talk to about types of lighting and lamps, sizes of motors, sizes of air conditioners and space heaters, and electrical loads of specialized process equipment. Finally, the maintenance staff must be interviewed to find the equipment and performance problems.

  1. Initial Walk through Tour

An initial facility/plant tour should be conducted by the facility/ plant manager, and should allow the auditor or audit team to see the major operational and equipment features of the facility. The main purpose of the initial tour is to obtain general information, and to obtain a general understanding of the facility’s operation. More specific information should be obtained from the maintenance and operational people during a second and more detailed data collection tour.

  1. Identification of EMO’S

As the audit is being conducted, the auditor should take notes on potential EMOs that are evident. As a general rule, the greatest effort should be devoted to analyzing and implementing the EMOs which show the greatest savings, and the least effort to those with the smallest savings potential. Therefore, the largest energy and cost activities should be examined carefully to see where savings could be achieved. Identifying EMOs requires a good knowledge of the available energy efficiency technologies that can accomplish the same job with less energy and less cost. For example, over-lighting indicates a potential lamp removal or lamp change EMO, and inefficient lamps indicate a potential lamp technology change. Motors with high use times are potential EMOs for high efficiency replacements. Notes on waste heat sources should indicate what other heating sources they might replace, and how far away they are from the end use point. Identifying any potential EMOs during the walk-through will make it easier later on to analyze the data and to determine the final EMO recommendations.

  1. Energy Audit Report

The next step in the energy audit process is to prepare a report which details the final results of the energy analyses and provides energy cost saving recommendations. The length and detail of this report will vary depending on the type of facility audited. A residential audit may result in a computer printout from the utility. An industrial audit is more likely to have a detailed explanation of the EMOs and benefit-cost analyses. The following discussion covers the more detailed audit reports. The report should begin with an executive summary that provides the owners/managers of the audited facility with a brief synopsis of the total savings available and the highlights of each EMO. The report should then describe the facility that has been audited, and provide information on the operation of the facility that relates to its energy costs. The energy bills should be presented, with tables and plots showing the costs and consumption. Following the energy cost analysis, the recommended EMOs should be presented, along with the calculations for the costs and benefits, and the cost-effectiveness criterion. Regardless of the audience for the audit report, it should be written in easy format.

Energy Audit Report Format:

  • Executive Summary

A brief summary of the recommendations and cost savings

  • Table of Contents
  • Introduction

Purpose of the energy audit

Need for a continuing energy cost control program

  • Facility Description

Product or service, and materials flow

Size, construction, facility layout, and hours of operation

Equipment list, with specifications

  • Energy Bill Analysis

Utility rate structures

Tables and graphs of energy consumptions and costs

Discussion of energy costs and energy bills

  • Energy Management Opportunities

Listing of potential EMOs

Cost and savings analysis

Economic evaluation

  • Energy Action Plan

Recommended EMOs and an implementation schedule

Designation of an energy monitor and ongoing program

  • Conclusion

Additional comments not otherwise

  1. The Energy Action Plan

An important part of the energy audit report is the recommended action plan for the facility. Some companies will have an energy audit conducted by their electric utility or by an independent consulting firm, and will then make changes to reduce their energy bills. They may not spend any further effort in the energy cost control area until several years in the future when another energy audit is conducted. In contrast to this is the company which establishes a permanent energy cost control program, and assigns one person—or a team of people—to continually monitor and improve the energy efficiency and energy productivity of the company. Similar to a Total Quality Management program where a company seeks to continually improve the quality of its products, services and operation, an energy cost control program seeks continual improvement in the amount of product produced for a given expenditure for energy. The energy action plan lists the EMOs which should be implemented first, and suggests an overall implementation schedule. Often, one or more of the recommended EMOs provides an immediate or very short payback period, so savings from that EMO—or those EMOs—can be used to generate capital to pay for implementing the other EMOs. In addition, the action plan also suggests that a company designate one person as the energy monitor or energy manager for the facility if it has not already done so. This person can look at the monthly energy bills and see whether any unusual costs are occurring, and can verify that the energy savings from EMOs is really being seen. Finally, this person can continue to look for other ways the company can save on energy costs, and can be seen as evidence that the company is interested in a future program of energy cost control.

Implementation:

After the energy consumption data has been collected and analyzed, the energy-related systems have been carefully examined, the ideas for improvement have been collected, and management commitment has been obtained, the next steps are to obtain company support for the program, to choose goals, and to initiate action.

  1. Energy Action Team

Now that the preliminary audits have uncovered some energy management measures that can save significant amounts of money or can substantially improve production, funding for the changes and employee support are two additional critical ingredients for success. These can best be obtained with the help of a committee, preferably called something like the energy action team.

No program will work within a company without employee support, particularly such a program as energy management which seems to promise employee discomfort at no visible increase in production. Therefore, one function of the energy action committee is to give representation to every important political group within the company. For this purpose, the committee must include people from unions, management, and every major group that could hinder the implementation of an energy management plan. The committee must also include at least one person with financial knowledge of the company, a person in charge of the daily operation of the facility, and line personnel in each area of the facility that will be affected by energy management.

  1. Goals

At least three different kinds of goals can be identified. First, performance goals, such as a reduction of 10 percent in Btu/unit product, can be chosen. Such goals should be modest at first so that they can be accomplished— in general, 10-30 percent reduction in energy usage for companies with little energy management experience and 8-15 percent for companies with more. These goals can be accompanied by goals for the reduction of projected energy costs by a similar amount. The more experienced the company is in energy management, the fewer easy saving possibilities exist; thus lower goals are more realistic in that case.

A second type of goal that can be established is an accounting goal. The ultimate objective in an energy accounting system is to be able to allocate the cost of energy to a product in the same way that other direct costs are allocated, and this objective guides the establishment of preliminary energy accounting goals. A preliminary goal would therefore be to determine the amount of electricity and the contribution to the electrical peak from each of the major departments within the company. This will probably require some additional metering, but the authors have found that such metering pays for itself in energy saving (induced by a better knowledge of the energy consumption patterns) in six months or less.

The third type of goal is that of employee participation. Even if an energy management program has the backing of the management, it will still fail without the support and participation of the employees. Ways to measure this include the number of suggestions per month; the dollar value of improvements adopted as a result of employee suggestions, per month; and the number of lights left on or machines left running unnecessarily, on a spot inspection. Work sampling has been used to estimate the percentage of time that people are working at various tasks—it can be used equally well on machines.

  1. Implementing Recommendations

In addition to providing and evaluating ideas, setting goals, and establishing employee support, the energy action committee has the duty of implementing the most promising ideas that have emerged from the energy evaluation process. Members of the committee have the responsibility to see that people are assigned to each project, that timetables are established, that money is assigned, and that progress reporting procedures are set up and followed.

  1. Monitoring

Energy management is not complete without monitoring and its associated feedback, and neither is the energy audit process. In an energy audit, monitoring discloses what measures contributed toward the company goals, what measures were counterproductive, and whether the goals themselves were too low or too high. Monitoring consists of collecting and interpreting data. The data to collect are defined by the objectives chosen by the energy action committee. At the very least, the electrical and gas bills and those of other relevant energy sources must be examined and their data graphed each month. Monthly graphs should include: the total energy used of each type (kWh of electricity, therms [105 Btu] of gas, etc.); the peaks, if they determine part of the cost of electricity or gas; and any other factors that contribute to the bills. At the same time, other output-related measures, such as Btu/ ton, should also be calculated, recorded, and graphed. The monitoring data should provide direct feedback to those most able to implement the changes. Often this requires that recording instruments be installed in a number of departments in addition to the meters required by the utility company. The additional expense is justified by increased employee awareness of the timing and amounts of energy consumed, and usually this awareness leads to a reduction in energy costs.

Metering at each department also enables management to determine where the energy is consumed and, possibly, what is causing the energy consumption. Such metering also helps each department manager to understand and control the consumption of his or her own department. Monitoring should result in more action. Find what is good, and copy it elsewhere. Find what is bad, and avoid it elsewhere. If the goals are too high, lower them. If the goals are too low, raise them. Wherever the difference between the planned objectives and the achievements is great, initiate an analysis to determine the reasons and then develop new objectives, initiate new action, and monitor the new results. In this way, the analysis, action, and monitoring process repeat itself.

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more about energy audit.

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energy management

Energy Management Opportunities in Thermal Power Plant:

The major energy management systems in thermal power plant are;

The Boiler And Steam Distribution System:

boiler burns fuel to produce heat that converts water into steam, and the steam distribution system takes the steam from the boiler to the point of use. Boilers consume much of the fuel used in many production facilities. The boiler is thus the first place to look when attempting to reduce natural gas or oil consumption. The steam distribution system is also a very important place to look for energy savings, since every pound of steam lost is another pound of steam that the boiler must produce.

The Heating, Ventilating, And Air Conditioning System:

All heating, air conditioning and ventilation (HVAC) equipment should be inventoried. Prepared data sheets can be used to record type, size, model numbers, age, electrical specifications or fuel use specifications, and estimated hours of operation. The equipment should be inspected to determine the condition of the evaporator and condenser coils, the air filters, and the insulation on the refrigerant lines. Air velocity measurements may also be made and recorded to assess operating efficiencies or to discover conditioned air leaks. This data will allow later analysis to examine alternative equipment and operations that would reduce energy costs for heating, ventilating, and air conditioning.

The Electrical Supply System:

This system consists of transformers, wiring, switches, and fuses— all the components needed to enable electricity to move from the utility owned wires at the facility boundary to its point of use within the company. By our definition, this supply system does not include lights, motors, or electrical controls. Most energy problems associated with the distribution of electricity are also safety problems, and solving the energy problems helps to solve the safety-related problems.

Electricity from a utility enters a facility at a service transformer. The area around the transformer should be dry, the transformer fins should be free from leaves and debris so that they can perform their cooling function and the transformer should not be leaking oil. If a transformer fails to meet any one of these conditions there is a serious problem which should justify a call to the local electrical utility, or, if the transformer is company owned, to the person or department in charge of maintaining the electrical system. 

upper mentioned energy management systems for better efficiencies.

Similarly Insulation Systems, Waste heat recovery, Energy Control systems, Energy system maintenance etc.

for further study:

https://www.ibm.com/topics/energy-management

for your further interest:

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Boiler

Introduction to Boiler

  A boiler is an enclosed vessel that provides a means for combustion heat to be transferred into water until it becomes heated water or steam. The hot water or steam under pressure is then usable for transferring the heat to a process. Water is a useful and cheap medium for transferring heat to a process. When water is boiled into steam its volume increases about 1,600 times, producing a force that is almost as explosive as gunpowder. This causes the boiler to be extremely dangerous equipment that must be treated with utmost care. The process of heating a liquid until it reaches its gaseous state is called evaporation. Heat is transferred from one body to another by means of:

  1.             Radiation, which is the transfer of heat from a hot body to a cold body without a conveying medium
  2.             Convection, the transfer of heat by a conveying medium, such as air or water

III.            Conduction, transfer of heat by actual physical contact, molecule to molecule

Boilers Specification:

The heating surface is any part of the boiler metal that has hot gases of combustion on one side and water on the other. Any part of the boiler metal that actually contributes to making steam is heating surface. The amount of heating surface of a boiler is expressed in square meters. The larger the heating surface a boiler has, the more efficient it becomes. The quantity of the steam produced is indicated in tons of water evaporated to steam per hour. Maximum continuous rating is the hourly evaporation that can be maintained for 24 hours. F & A means the amount of steam generated from water at 100°C to saturated steam at 100°C.

Boilers Systems:

The boiler system comprises of: feed water system, steam system and fuel system. The feed water system provides water to the boiler and regulates it automatically to meet the steam demand. Various valves provide access for maintenance and repair. The steam system collects and controls the steam produced in the boiler. Steam is directed through a piping system to the point of use. Throughout the system, steam pressure is regulated using valves and checked with steam pressure gauges. The fuel system includes all equipment used to provide fuel to generate the necessary heat. The equipment required in the fuel system depends on the type of fuel used in the system

The water supplied to the boiler that is converted into steam is called feed water. The two sources of feed water are:

  1.             Condensate or condensed steam returned from the processes and
  2.             Makeup water (treated raw water) which must come from outside the boiler room and plant processes.

For higher boiler efficiencies, the feed water is preheated by economizer, using the waste heat in the flue gas.

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reading more about boilers: 

https://www.britannica.com/technology/boiler

Types of boilers

There are virtually infinite numbers of boiler designs but generally they fit into one of two categories: here are types of boiler as below:

1. Fire Tube Boilers:

types of boiler

  Fire tube or “fire in tube” boilers; contain long steel tubes through which the hot gasses from a furnace pass and around which the water to be converted to steam circulates (Figure 4.2). Fire tube boilers, typically have a lower initial cost, are more fuel efficient and easier to operate, but they are limited generally to capacities of 25 tons/hr and pressures of17.5 kg/cm2

2 .Water Tube Boilers:

water tube boiler
water tube boiler

Water tube or “water in tube” boilers are those in which the conditions are reversed with the water passing through the tubes and the hot gasses passing outside the tubes (Figure 4.3). These boilers can be of single- or multiple-drum type. These boilers can be built to any steam capacities and pressures, and have higher efficiencies than fire tube boilers.

  1.    Packaged Boiler

one of the types of boiler is called packaged boiler because it comes as a complete package.  Once delivered to site, it requires only the steam, water pipe work, fuel supply and electrical connections to be made for it to become operational. Package boilers are generally of shell type with fire tube design so as to achieve high heat transfer rates by both radiation and convection

The features of package boilers are:

Small combustion space and high heat release rate resulting in faster evaporation.

  1.             Large number of small diameter tubes leading to good convective heat transfer.

III.            Forced or induced draft systems resulting in good combustion efficiency.

  1.             Number of passes resulting in better overall heat transfer.
  2.             Higher thermal efficiency levels compared with other boilers.

These boilers are classified based on the number of passes – the number of times the hot combustion gases pass through the boiler. The combustion chamber is taken, as the first pass after which there may be one, two or three sets of fire-tubes. The most common boiler of this class is a three-pass unit with two sets of fire-tubes and with the exhaust gases exiting through the rear of the boiler.

4.    Stoker Fired Boiler: types of boilers

one of types of boiler is Stokers , classified according to the method of feeding fuel to the furnace and by the type of grate. The main classifications are:

  1. Chain-grate or traveling-grate stoker
  2. Spreader stoker
  1. Chain-Grate or Traveling-Grate Stoker Boiler

Coal is fed onto one end of a moving steel chain grate. As grate moves     along the length of the furnace, the coal burns before dropping off at the end as ash. Some degree of skill is required, particularly when setting up the grate, air dampers and baffles, to ensure clean combustion leaving minimum of un burnt carbon in the ash.

  The coal-feed hopper runs along the entire coal-feed end of the furnace. A coal grate is used to control the rate at which coal is fed into the furnace, and to control the thickness of the coal bed and speed of the grate. Coal must be uniform in size, as large lumps will not burn out completely by the time they reach the end of the grate. As the bed thickness decreases from coal feed end to rear end, different amounts of air are required- more quantity at coal-feed end and less at rear end.

  1. Spreader Stoker Boiler

Spreader stokers utilize a combination of suspension burning and grate burning. The coal is continually fed into the furnace above a burning bed of coal. The coal fines are burned in suspension; the larger particles fall to the grate, where they are burned in a thin, fast burning coal bed. This method of firing provides good flexibility to meet load fluctuations, since ignition is almost instantaneous when firing rate is increased. Hence, the             spreader stoker is favored over other types of stokers in many industrial applications.

5.    Pulverized Fuel Boiler

Most coal-fired power station boilers use pulverized coal, and many of the larger industrial water-tube boilers also use this pulverized fuel. This technology is well developed, and there are thousands of units around the world, accounting for well over 90% of coal-fired capacity. The coal is ground (pulverized) to a fine powder, so that less than 2% is +300 micro meter (μm) and 70-75% is below 75 microns, for a bituminous coal. It should be noted that too fine a powder is wasteful of grinding mill power. On the other hand, too coarse a powder does not burn completely in the combustion chamber and results in higher un burnt losses.

The pulverized coal is blown with part of the combustion air into the boiler plant through a series of burner nozzles. Secondary and tertiary air may also be added. Combustion takes place at temperatures from 1300-1700°C, depending largely on coal grade. Particle residence time in the boiler is typically 2 to 5 seconds, and the particles must be small enough for complete combustion to have taken place during this time. This system has many advantages such as ability to fire varying quality of coal, quick responses to changes in load, use of high pre-heat air temperatures etc. One of the most popular systems for firing pulverized coal is the tangential firing using four burners corner to corner to create a fireball at the center of the furnace

6. FBC Boiler: types of boilers

When an evenly distributed air or gas is passed upward through a finely divided bed of solid particles such as sand supported on a fine mesh, the particles are undisturbed at low velocity. As air velocity is gradually increased, a stage is reached when the individual particles are suspended in the air stream. Further, increase in velocity gives rise to bubble formation, vigorous turbulence and rapid mixing and the bed is said to be fluidized. If the sand in a fluidized state is heated to the ignition temperature of the coal and the coal is injected continuously in to the bed, the coal will burn rapidly, and the bed attains a uniform temperature due to effective mixing. Proper air distribution is vital for maintaining uniform fluidization across the bed. Ash is disposed by dry and wet ash disposal systems. Fluidized bed combustion has significant advantages over conventional firing systems and offers multiple benefits namely fuel flexibility, reduced emission of noxious pollutants such as SOx and NOx, compact boiler design and higher combustion efficiency.

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https://www.britannica.com/technology/steam-engine

Boiler performance

Boiler performance

The boiler performance parameters of boiler, like efficiency and evaporation ratio reduces with time due to poor combustion, heat transfer surface fouling and poor operation and maintenance. Even for a new boiler, reasons such as deteriorating fuel quality, water quality etc. can result in poor boiler performance. Boiler efficiency tests help us to find out the deviation of boiler efficiency from the best efficiency and target problem area for corrective action.

Boiler performance or Efficiency:

Thermal efficiency of boiler is defined as the percentage of heat input that is effectively utilized to generate steam. There are two methods of assessing boiler efficiency.

  1. a)The Direct Method: Where the energy gain of the working fluid (water and steam) is compared with the energy content of the boiler fuel.
  2. b)The Indirect Method: Where the efficiency is the difference between the losses and the energy input.
  1. a)Direct Method

This is also known as ‘input-output method’ due to the fact that it needs only the useful output (steam) and the heat input (i.e. fuel) for evaluating the efficiency. This efficiency can be evaluated using the formula

Boiler Efficiency = (Heat Output/Heat Input) * 100                     

Parameters to be monitored for the calculation of boiler efficiency by direct method are :

  • Quantity of steam generated per hour (Q) in kg/hr.
  • Quantity of fuel used per hour (q) in kg/hr.
  • The working gauge pressure (in kg/cm2) and superheat temperature (°C), if any
  • The temperature of feed water (°C)
  • Type of fuel and gross calorific value of the fuel (GCV) in kCal/kg of fuel

Boiler efficiency = Q x (hg-hf) ×100 /(q×GCV)

Where,

hg – Enthalpy of saturated steam in kCal/kg of steam

hf – Enthalpy of feed water in kCal/kg of water

It should be noted that boiler may not generate 100% saturated dry steam, and there may be some amount of wetness in the steam.

Advantages of Direct Method:

  • Plant people can evaluate quickly the efficiency of boilers
  • Requires few parameters for computation
  • Needs few instruments for monitoring
  1. Disadvantages of Direct Method:

  • Does not give clues to the operator as to why efficiency of system is lower
  • Does not calculate various losses accountable for various efficiency levels
  1. b)Indirect Method:

There are reference standards for Boiler performance Testing at Site using indirect method namely British Standard, BS 845: 1987 and USA Standard is ASME PTC-4-1 Power Test Code Steam Generating Units’. Indirect method is also called as ‘’heat loss method’’. The efficiency can be arrived at, by subtracting the heat loss fractions from 100. The standards do not include blow down loss in the efficiency determination process. A brief procedure for calculating boiler efficiency by indirect method is given below.

The principle losses that occur in a boiler are:

  1. Loss of heat due to dry flue gas
  2. Loss of heat due to moisture in fuel and combustion air
  3. Loss of heat due to combustion of hydrogen
  4. Loss of heat due to radiation
  5. Loss of heat due to unburnt

In the above, loss due to moisture in fuel and the loss due to combustion of hydrogen are dependent on the fuel, and cannot be controlled by design. The data required for calculation of boiler efficiency using indirect method are:

  • Ultimate analysis of fuel (H2, O2, S, C, moisture content, ash content)
  • Percentage of Oxygen or CO2in the flue gas
  • Flue gas temperature in °C (Tf)
  • Ambient temperature in °C (Ta) & humidity of air in kg/kg of dry air
  • GCV of fuel in kCal/kg
  • Percentage combustible in ash (in case of solid fuels)
  • GCV of ash in kCal/kg (in case of solid fuels)

With the help of these parameters the boiler engineers find the losses using standard approaches as specified by ASME and other boiler OEMs. Finally losses can be subtracted from the heat added and hence efficiency can be found.

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Boiler blowdown

Boiler blowdown

When water is boiled and steam is generated, any dissolved solids contained in the water remain in the boiler. If more solids are put in with the feed water, they will concentrate and may eventually reach a level where their solubility in the water is exceeded and they deposit from the solution. Above a certain level of concentration, these solids encourage foaming and cause carryover of water into the steam. The deposits also lead to scale formation inside the boiler, resulting in localized overheating and finally causing boiler tube failure. It is, therefore, necessary to control the level of concentration of the solids and this is achieved by the process of ‘blowing down’, where a certain volume of water is blown off and is automatically replaced by feed water – thus maintaining the optimum level of total dissolved solids (TDS) in the boiler water. Blow down is necessary to protect the surfaces of the heat exchanger in the boiler. However, blow down can be a significant source of heat loss, if improperly carried out. The maximum amount of total dissolved solids (TDS) concentration permissible in various types of boilers is given in Table 4.1.

Recommended TDS Levels For Various Boilers

Boiler Type Maximum TDS (ppm)
1. Lancashire 10,000
2. Smoke and water tube boilers (12 kg/cm2) 5,000
3. Low pressure Water tube boiler 2000–3000
4. High Pressure Water tube boiler with super heater 3,000–3,500
5. Package and economic boilers 3,000
6. Coil boilers and steam generators 2000 (in the feed water)

Conductivity as Indicator of Boiler Water Quality

Since it is tedious and time consuming to measure total dissolved solids (TDS) in boiler water system, conductivity measurement is used for monitoring the overall TDS present in the boiler. A rise in conductivity indicates a rise in the “contamination” of the boiler water. Conventional methods for blowing down the boiler depend on two kinds of blowdown –intermittent and continuous

  1.             Intermittent Blowdown:

The intermittent blown down is given by manually operating a valve fitted to discharge pipe at the lowest point of boiler shell to reduce parameters (TDS or conductivity, pH, Silica and Phosphates concentration) within prescribed limits so that steam quality is not likely to be affected. In intermittent blowdown, a large diameter line is opened for a short period of time, the time being based on a thumb rule such as “once in a shift for 2 minutes”. Intermittent blowdown requires large short-term increases in the amount of feed water put into the boiler, and hence may necessitate larger feed water pumps than if continuous blowdown is used. Also, TDS level will be varying, thereby causing fluctuations of the water level in the boiler due to changes in steam bubble size and distribution which accompany changes in concentration of solids. Also substantial amount of heat energy is lost with intermittent blowdown.

2.            Continuous Blowdown: 

There is a steady and constant dispatch of small stream of concentrated boiler water, and replacement by steady and constant inflow of feed water. This ensures constant TDS and steam

Even though large quantities of heat are wasted, opportunity exists for recovering this heat by blowing into a flash tank and generating flash steam. This flash steam can be used for preheating boiler feed water or for any other purpose (see Figure 9 for blowdown heat recovery system). This type of blow down is common in high-pressure boilers

Boiler Blowdown Calculations:

The quantity of blow down required to control boiler water solids concentration is calculated by using the following formula:

Blow down (%) = 

                       (Feed water (TDS) ×  % Make Up Water)/Maximum Permissible TDS in the Boiler

If maximum permissible limit of TDS as in a package boiler is 3000 ppm, percentage make up water is 10% and TDS in feed water is 300 ppm, then the percentage blowdown is given as:

                                    = 300 x 10/ 3000

                                    = 1%

If boiler evaporation rate is 3000 kg/hr then required blowdown rate is:

                                      =        3000 x 1/100

                                       = 30 kg/hr

Benefits of Boiler Blowdown: 

Good boiler blowdown control can significantly reduce treatment and operational costs that include:

  • Lower pretreatment costs
  • Less make-up water consumption
  • Reduced maintenance downtime
  • Increased boiler life
  • Lower consumption of treatment chemicals

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water treatment

Boiler Water Treatment

Producing quality steam on demand depends on properly managed water treatment to control steam purity, deposits and corrosion. A boiler is the sump of the boiler system. It ultimately receives all of the pre-boiler contaminants. Boiler performance, efficiency, and service life are direct products of selecting and controlling feed water used in the boiler. When feed water enters the boiler, the elevated temperatures and pressures cause the components of water to behave differently. Most of the components in the feed water are soluble. However, under heat and pressure most of the soluble components come out of solution as particulate solids, sometimes in crystallized forms and other times as amorphous particles. When solubility of a specific component in water is exceeded, scale or deposits develop. The boiler water must be sufficiently free of deposit forming solids to allow rapid and efficient heat transfer and it must not be corrosive to the boiler metal.

1  Deposit Control

Deposits in boilers may result from hardness contamination of feed water and corrosion products from the condensate and feed water system. Hardness contamination of the feed water may arise due to deficient softener system. Deposits and corrosion result in efficiency losses and may result in boiler tube failures and inability to produce steam. Deposits act as insulators and slow heat transfer. Large amounts of deposits throughout the boiler could reduce the heat transfer enough to reduce the boiler efficiency significantly. Different type of deposits affects the boiler efficiency differently. Thus it may be useful to analyse the deposits for its characteristics. The insulating effect of deposits causes the boiler metal temperature to rise and may lead to tube-failure by overheating.

2  Impurities Causing Deposits

The most important chemicals contained in water that influences the formation of deposits in the boilers are the salts of calcium and magnesium, which are known as hardness salts. Calcium and magnesium bicarbonate dissolve in water to form an alkaline solution and these salts are known as alkaline hardness. They decompose upon heating, releasing carbon dioxide and forming a soft sludge, which settles out. These are called temporary hardness-hardness that can be removed by boiling. Calcium and magnesium sulphates, chlorides and nitrates, etc. when dissolved in water are chemically neutral and are known as non-alkaline hardness. These are called permanent hardness and form hard scales on boiler surfaces, which are difficult to remove. Non-alkalinity hardness chemicals fall out the solution due to reduction in solubility as the temperature rises, by concentration due to evaporation which takes place within the boiler, or by chemical change to a less soluble compound.

3  Silica

The presence of silica in boiler water can rise to formation of hard silicate scales. It can also associate with calcium and magnesium salts, forming calcium and magnesium silicates of very low thermal conductivity. Silica can give rise to deposits on steam turbine blades, after been carried over either in droplets of water in steam, or in volatile form in steam at higher pressures. Two major types of boiler water treatment are: Internal water treatment and External water treatment.

4  Internal Water Treatment

Internal treatment is carried out by adding chemicals to boiler to prevent the formation of scale by converting the scale-forming compounds to free-flowing sludges, which can be removed by blowdown. This method is limited to boilers, where feed water is low in hardness salts, to low pressures- high TDS content in boiler water is tolerated, and when only small quantity of water is required to be treated. If these conditions are not applied, then high rates of blowdown are  required to dispose off the sludge. They become uneconomical from heat and water loss consideration.

Different waters require different chemicals. Sodium carbonate, sodium aluminate, sodium phosphate, sodium sulphite and compounds of vegetable or inorganic origin are all used for this purpose. Proprietary chemicals are available to suit various water conditions. The specialist

must be consulted to determine the most suitable chemicals to use in each case. Internal treatment alone is not recommended.

5  External Water Treatment

External treatment is used to remove suspended solids, dissolved solids (particularly the calcium and magnesium ions which is a major cause of scale formation) and dissolved gases (oxygen and carbon dioxide). The external treatment processes available are: ion exchange; demineralization; reverse osmosis and de-aeration. Before any of these are used, it is necessary to remove suspended solids and colour from the raw water, because these may foul the resins used in the subsequent treatment sections.

Methods of pre-treatment include simple sedimentation in settling tanks or settling in clarifiers with aid of coagulants and flocculants. Pressure sand filters, with spray aeration to remove carbon dioxide and iron, may be used to remove metal salts from bore well water.

The first stage of treatment is to remove hardness salt and possibly non-hardness salts. Removal of only hardness salts is called softening, while total removal of salts from solution is called demineralization.

The processes are:-

Ion-exchange process (Softener Plant):

In ion-exchange process, the hardness is removed as the water passes through bed of natural zeolite or synthetic resin and without the formation of any precipitate. The simplest type is ‘base exchange’ in which calcium and magnesium ions are exchanged for sodium ions. After saturation regeneration is done with sodium chloride. The sodium salts being soluble, do not form scales in boilers. Since base exchanger only replaces the calcium and magnesium with sodium, it does not reduce the TDS content, and blowdown quantity. It also does not reduce the alkalinity. Demineralization is the complete removal of all salts. This is achieved by using a “cation” resin, which exchanges the cations in the raw water with hydrogen ions, producing hydrochloric, sulphuric and carbonic acid. Carbonic acid is removed in degassing tower in which air is blown through the acid water. Following this, the water passes through an “anion” resin which exchanges anions with the mineral acid (e.g. sulphuric acid) and forms water. Regeneration of cations and anions is necessary at intervals using, typically, mineral acid and caustic soda respectively. The complete removal of silica can be achieved by correct choice of anion resin.

Ion exchange processes can be used for almost total demineralization if required, as is the case in large electric power plant boilers

De-aeration:

In de-aeration, dissolved gases, such as oxygen and carbon dioxide, are expelled by preheating the feed water before it enters the boiler. All natural waters contain dissolved gases in solution. Certain gases, such as carbon dioxideand oxygen, greatly increase corrosion. When heated in boiler systems, carbon dioxide (CO2) and oxygen (O2) are released as gases and combine with water (H2O) to form carbonic acid, (H2CO3).

Removal of oxygen, carbon dioxide and other non-condensable gases from boiler feedwater is vital to boiler equipment longevity as well as safety of operation. Carbonic acid corrodes metal reducing the life of equipment and piping. It also dissolves iron (Fe) which when returned to the boiler precipitates and causes scaling on the boiler and tubes. This scale not only contributes to reducing the life of the equipment but also increases the amount of energy needed to achieve heat transfer. Deaeration can be done by mechanical deaeration-aeration, by chemical de-deration or by both together.

Mechanical deaeration for water treatment:

Mechanical deaeration for the removal of these dissolved gases is typically utilized prior to the addition of chemical oxygen scavengers. Mechanical deaeration is based on Charles’ and Henry’s laws of physics. Simplified, these laws state that removal of oxygen and carbon dioxide can be accomplished by heating the boiler feed water, which reduces the concentration of oxygen and carbon dioxide in the atmosphere surrounding the feed water. Mechanical de-aeration can be the most economical. They operate at the boiling point of water at the pressure in the deaerator. They can be of vacuum or pressure type.

The vacuum type of de-aerator operates below atmospheric pressure, at about 82 °C, can reduce the oxygen content in water to less than 0.02 mg/litre. Vacuum pumps or steam ejectors are required to maintain the vacuum.

The pressure-type de-aerators operates by allowing steam into the feed water through a pressure control valve to maintain the desired operating pressure, and hence temperature at a minimum of 105 °C. The steam raises the water temperature causing the release of O2 and CO2 gases that are then vented from the system. This type can reduce the oxygen content to 0.005 mg/litre.

Where excess low-pressure steam is available, the operating pressure can be selected to make use of this steam and hence improve fuel economy. In boiler systems, steam is preferred for de-aeration because:

  1.             Steam is essentially free from O2 and CO2,
  2.             Steam is readily available

III.            Steam adds the heat required to complete the reaction.

c:

While the most efficient mechanical deaerators reduce oxygen to very low levels (0.005 mg/litre), even trace amounts of oxygen may cause corrosion damage to a system. Consequently, good operating practice requires removal of that trace oxygen with a chemical oxygen scavenger such as sodium sulfite or hydrazine. Sodium sulphite reacts with oxygen to form sodium sulphate, which increases the TDS in the boiler water and hence increases the blowdown requirements and make-up water quality. Hydrazine reacts with oxygen to form nitrogen and water. It is invariably used in high pressures boilers when low boiler water solids are necessary, as it does not increase the TDS of the boiler water.

Reverse Osmosis for water treatment:

Reverse osmosis uses the fact that when solutions of differing concentrations are separated by a semi-permeable membrane, water from less concentrated solution passes through the membrane to dilute the liquid of high concentration. If the solution of high concentration is pressurized, the process is reversed and the water from the solution of high concentration flows to the weaker solution. This is known as reverse osmosis. The quality of water produced depends upon the concentration of the solution on the high-pressure side and pressure differential across the membrane. This process is suitable for waters with very high TDS, such as sea water.

The semi-permeable nature of the membrane allows the water to pass much

more readily than the dissolved minerals. Since the water in the less concentrated solution seeks to dilute the more concentrated solution, the water passage through the membrane generates a noticeable head difference between the two solutions. This head difference is a measure of the concentration difference of the two solutions and is referred to as the osmotic pressure difference.

When a pressure is applied to the concentrated solution which is great that the osmotic pressure difference, the direction of water passage through the membrane is reversed and the process that we refer to as reverse osmosis is established. That is, the membrane’s ability to selectively pass water is unchanged, only the direction of the water flow is changed.

The feed water and concentrate (reject stream) ports illustrates a continuously operating RO system.

Recommended boiler and feed water quality for water treatment:

The impurities found in boiler water depend on the untreated feed water quality, the treatment process used and the boiler operating procedures. As a general rule, the higher the boiler operating pressure, the greater will be the sensitivity to impurities. Recommended feed water and boiler water limits are shown in Table 4.2 and Table 4.3.

Recommended Feed Water Limits

Factor Upto 20 kg/cm2 21 – 39 kg/cm2 41 – 59 kg/cm2
Total iron (ppm) 0.05 0.02 0.01
Total copper (ppm) 0.01 0.01 0.01
Total silica (ppm) 1.0 0.3 0.1
Oxygen (ppm) 0.02 0.02 0.01
Hydrazine residual ppm 0.02-0.04
pH at 25°C 8.8-9.2 8.8-9.2 8.02-9.2
Hardness, ppm 1.0 0.5

Recommended Boiler Water Limits   (Is 10392, Year 1982)

Factor Upto 20 kg/cm2   21 – 39 kg/cm2 40 – 59 kg/cm2
TDS, ppm 3000-3500 1500-2500 500-1500
Total iron dissolved solids ppm 500 200 150
Specific electrical conductivity 1000 400 300

at 25°C (mho)

1000 400 300
Phosphate residual ppm 20-40 20-40 15-25
pH at 25°C 10-10.5 10-10.5 9.8-10.2
Silica (max) ppm 25 15 10

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Rankine cycle

Ideal rankine cycle

1-2: Isentropic expansion of superheated steam in the turbine.

2-3: Condensation in the condenser which converts steam into water. It is the constant pressure and constant
temperature heat rejection from steam which causes condensation. The volume is reduced about 1000 time in the condenser, thus saving huge amount of mechanical work.

rankine cycle
ideal rankine cycle

3-4: Constant entropy pressure rise in the pump.

4-5: There is constant pressure heat supply in the economizer or with feed water heating.

5-6: Heat supply at constant temperature and pressure in the Boiler.

6-1: The steam is superheated at constant pressure.

4-5-6-1 ; This is the line of constant pressure.

5-6: Is the line of constant Temperature.

After expansion inside the turbine, the dryness fraction is kept more than 0.85, as high water content causes damage like rust etc.

To reduce mechanical work for pumping, we cool until saturated liquid is obtained and no steam content remains.

Actual rankine cycle

In actual Rankine cycle, the processes are deviated from those of Ideal Rankine cycle.
Solid lines are showing ideal processes and dotted lines are showing actual processes.

rankine cycle
actual rankine cycle

1’-2’: Actual adiabatic expansion of superheated steam in the turbine. Turbine is surrounded by insulating material such as fiber glass or asbestos to prevent heat loss.

2’-3’: Actual process of condensation.

3’-4’: Adiabatic rise in pressure in the pump.

S’2 is higher than S2 and S4 is higher than S4, showing that entropy is generated in these processes.

Isentropic Efficiency
 = Actual work/ Ideal work when expansion is isentropic.

Unfortunately, the entropy is generated in cases, the expansion and the compression.

4’-5’: Heating in the economizer.

5’-6’: Actual process of heating in the boiler.

6’-1’: Super-heating process in the super heater.

It must be mentioned here that all the process in the Rankine Cycle are control volume as mass is entering and leaving and also the heat and work.

Ideal rankine Cycle is a Cycle in which all the thermodynamic processes go ideally without losses and there is no entropy generation during any of the process.

In the figure below, the actual rankine cycle is shown on the T-S diagram.

Reheat rankine cycle:

The drawback of having high pressure in the boiler is the increase of water content at the blades steam turbine. To avoid this problem, reheat Rankine cycle is used.
The diagram for the Reheat Rankine cycle is shown.

reheat rankine cycle
reheat rankine cycle

We can enhance the thermal efficiency of the steam turbine power plant by reheating the steam coming from high pressure turbine, approximately to same temperature as the inlet of the first turbine and then passing it from an another turbine operating at low pressure, called low pressure turbine. By this arrangement, the dryness fraction at the exit of low pressure turbine is increase which is desirable to increase the thermal efficiency of the Plant.

The various processes in Reheat Rankine Cycle are:

1-2: Isentropic Expansion of superheated steam in the high pressure turbine.

2-3: Constant pressure reheating in the Re-heater.

3-4: Isentropic expansion in low pressure turbine.

4-5: Heat rejection in the condenser at constant temperature and pressure.

5-6: Isentropic pressure rise in the Pump.

6-7: Heating of subcooled liquid

7-1: Constant Pressure Reheating in the Boiler.

Heat supplied to the Boiler = h1 – h6 = Q1

Heat rejected to the condenser = h4 – h5 = Q2

Total Work output = Wt1 + Wt2 = Work done in low pressure turbine + Work done in high pressure turbine = (h1 – h2) + (h3 – h4)

Total Heat supplied = heat supplied in the Boiler + Heat supplied in the Re-heater = (h1 -h6) + (h3 – h2)

Thermal efficiency = Net work output/ Total heat supplied = {(h1 – h2) + (h3 – h4) – (h6 – h5)}/ {(h1 -h2) + (h3 – h2)}.

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