Techniques Employed for Saving Energy | Essay | Energy Management

Read this essay to learn about the techniques employed for saving energy.

Essay # 1. Fluidized Bed Combustion Technology:

Fluidized bed combustion (FBC) is a combustion technology used in power plants. Fluidized beds suspend solid fuels in upward-blowing jets of air during the combustion process. The result is a turbulent mixing of gas and solids.

The tumbling action, much like a bubbling fluid, provides more effective chemical reactions and heat transfer. FBC technology was adapted to burn petroleum coke and coal mining waste for power generation in the early 1980s in the US. At that time, US regulations first provided special incentives to the use of renewable fuels and waste fuels.

FBC technology spread to other parts of the globe to address specific fuel quality problems. The technology has proved well suited to burning fuels that are difficult to ignite, like petroleum coke and anthracite, low quality fuels like high ash coals and coal mine wastes, and fuels with highly variable heat content, including biomass and mixtures of fuels.

The lower operating temperature of fluid-bed combustors reduces the quantity of pollutants produced and sulphur oxides can be retained if crushed dolomite or limestone is added to the bed. Fluid-beds can also be used for the incineration of municipal and industrial wastes at acceptably low levels of environmental pollution.

Shallow fluid-bed heat exchangers have particular advantage in recovering waste heat from gases. The advantageous thermal properties of fluidised solids could be exploited in energy storage schemes and offer an attractive medium for metallurgical heat treatment processes where previously more hazardous media have had to be used.

The technology burns fuel at temperatures of 1,400 to 1,700 °F (760 to 930 °C), a range where nitrogen oxide formation is lower than in traditional pulverized coal units. Fluidized-bed combustion evolved from efforts in Germany to control emissions from roasting sulphate ores without the need for external emission controls (such as scrubbers-flue gas desulfurization).

The mixing action of the fluidized bed brings the flue gases into contact with a sulphur-absorbing chemical, such as limestone or dolomite. More than 95% of the sulphur pollutants in the fuel can be captured inside the boiler by the sorbent. The sorbent also captures some heavy metals, though not as effectively as do the much cooler wet scrubbers on conventional units.

Commercial FBC units operate at competitive efficiencies, cost less than today’s units, and have NO₂ and SO₂ emissions below acceptable limit.

Types of Fluidized Bed Technologies and their potential advantages related to energy conservations:

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

a. FBC:

Atmospheric fluidized beds use limestone or dolomite to capture sulphur released by the combustion of coal. Jets of air suspend the mixture of sorbent and burning coal during combustion, converting the mixture into a suspension of red-hot particles that flow like a fluid. These boilers operate at atmospheric pressure.

b. PFBC:

The first-generation PFBC system also uses a sorbent and jets of air to suspend the mixture of sorbent and burning coal during combustion. However, these systems operate at elevated pressures and produce a high-pressure gas stream at temperatures that can drive a gas turbine. Steam generated from the heat in the fluidized bed is sent to a steam turbine, creating a highly efficient combined cycle system.

Advanced PFBC:

i. PFBC system increases the gas turbine firing temperature by using natural gas in addition to the vitiated air from the PFB combustor. This mixture is burned in a topping combustor to provide higher inlet temperatures for greater combined cycle efficiency. However, this uses natural gas, usually a higher priced fuel than coal.

ii. APFBC. In more advanced second-generation PFBC systems, a pressurized carbonizer is incorporated to process the feed coal into fuel gas and char. The PFBC burns the char to produce steam and to heat combustion air for the gas turbine. The fuel gas from the carbonizer burns in a topping combustor linked to a gas turbine, heating the gases to the combustion turbine’s rated firing temperature.

Heat is recovered from the gas turbine exhaust in order to produce steam, which is used to drive a conventional steam turbine, resulting in a higher overall efficiency for the combined cycle power output. These systems are also called APFBC, or advanced circulating pressurized fluidized-bed combustion combined cycle systems. An APFBC system is entirely coal-fueled.

iii. GFBCC (Gasification fluidized-bed combustion combined cycle systems): GFBCC, have a pressurized circulating fluidized-bed (PCFB) partial gasifier feeding fuel syngas to the gas turbine topping combustor. The gas turbine exhaust supplies combustion air for the atmospheric circulating fluidized-bed combustor that burns the char from the PCFB partial gasifier.

Advantages of Fluidized bed Combustion technology:

Fluidized bed combustion technology offers following advantages which are also helpful in energy conservation and environment protection point of view.

These are:

i. Helpful in burning the fuel which is difficult to ignite.

ii. Increased fuel efficiency.

iii. Less emission of pollutants.

iv. Fluid-beds can also be used for the incineration of municipal and industrial wastes at acceptably low levels of environmental pollution.

v. Sulphur pollutants in fuel can be captured and not emitted in the environment.

vi. Low quality fuel and biomass can be effectively used.

Essay # 2. Waste Heat Recovery:

Captured and reused waste heat is an emission free substitute for costly purchased fuels or electricity. Numerous technologies are available for transferring waste heat to a productive end use. Large amount of energy is wasted in various types of industrial waste. Therefore, there is an opportunity to recover this energy loss in industrial process waste to conserve the energy in every possible way.

Industrial waste heat refers to energy that is generated in industrial processes without being put to practical use. Sources of waste heat include hot combustion gases discharged to the atmosphere, heated products exiting industrial processes, and heat transfer from hot equipment surfaces.

The exact quantity of industrial waste heat is poorly quantified, but various studies have estimated that as much as 20 to 50% of industrial energy consumption is ultimately discharged as waste heat. While some waste heat losses from industrial processes are inevitable, facilities can reduce these losses by improving equipment efficiency or installing waste heat recovery technologies.

Waste heat recovery entails capturing and reusing the waste heat in industrial processes for heating or for generating mechanical or electrical work. Example uses for waste heat include generating electricity, preheating combustion air, preheating furnace loads, absorption cooling, and space heating.

Heat recovery technologies frequently reduce the operating costs for facilities by increasing their energy productivity. Many recovery technologies are already well developed and technically proven; however, there are numerous applications where heat is not recovered due to a combination of market and technical barriers.

A comprehensive investigation of waste heat losses, recovery practices, and barriers is required in order to better identify heat recovery opportunities and technology needs. Such an analysis can aid decision makers in identifying research priorities for promoting industrial energy efficiency.

Essential Components of waste heat recovery:

There are three essential components of waste heat recovery.

These are:

(1) Sources of waste heat:

i. Combustion exhaust.

ii. Process exhaust.

iii. Hot gases.

iv. Cooling tower water.

v. Process off gases. Steel electric arc furnace Aluminium reverberatory furnace

vi. Conductive, convective, and radiative losses from heated products.

(2) Recovery technology:

i. Regenerator.

ii. Recuperator.

iii. Economizers.

iv. Waste Heat Boilers.

v. Thermoelectric Generator.

(3) Recovered heat use:

i. Pre-heating (boiler feed water, raw material, combustion air).

ii. Electricity supply.

iii. Domestic hot water.

iv. Power generation.

v. Steam generation for use in: power generation mechanical power process steam.

vi. Space heating.

vii. Transfer to liquid or gaseous process stream.

For recovering the useful energy from waste, each waste heat stream should be investigated in terms of its waste heat quantity (the approximate energy contained in the waste heat stream), quality (typical exhaust temperatures), current recovery technologies and practices, and barriers to heat recovery.

Energy content of waste heat streams is a function of mass flow rate, composition, and temperature, and was evaluated based on process energy consumption, typical temperatures, and mass balances. Since waste heat temperature is an important quality in the feasibility of waste heat recovery, the study of exhaust temperatures of all waste heat sources must be carried out.

Additionally, the work potential or efficiency of converting waste heat to another form of energy (i.e., mechanical or electrical) should also be estimated. The work potential (based on Carnot efficiency) is a measure of the maximum energy that could be recovered by using the waste heat to drive a heat engine. Quantifying work potential allows a better comparison of waste heat sources with different exhaust temperatures.

Essay # 3. Microwave Heating:

Microwave heating, which uses electromagnetic energy in the frequency range 300- 3000 MHz, can be used successfully to heat many dielectric materials. Microwave heating is usually applied at the most popular of the frequencies allowed for ISM (industrial, scientific and medical) applications, namely 915 (896 in the UK) and 2450 MHz. Domestic microwave ovens are a familiar example operating at 2450 MHz.

The way in which a material will be heated by microwaves depends on its shape, size, dielectric constant and the nature of the microwave equipment used. In the microwave S-band range (2450 MHz), the dominant mechanism for dielectric heating is dipolar loss, also known as the re-orientation loss mechanism.

When a material containing permanent dipoles is subject to a varying electromagnetic field, the dipoles are unable to follow the rapid reversals in the field. As a result of this phase lag; power is dissipated in the material.

Although microwaves have been firstly adopted for communications scope, an increasing attention to microwave heating applications has been gained since World War II. Reasons for this growing interest can be found in the peculiar mechanism for energy transfer: during microwave heating, energy is delivered directly to materials through molecular interactions with electromagnetic field via conversion of electrical field energy into thermal energy. This can allow unique benefits, such as high efficiency of energy conversion and shorter processing times, thus reductions in manufacturing costs due to energy saving.

Advantages of microwave heating:

Peculiarity of microwave heating is the energy transfer. In conventional heating processes, energy is transferred to material by convection, conduction and radiation phenomena promoted by thermal gradients and through the materials external surface. While microwave energy is delivered directly to materials through molecular interactions (loss mechanisms) with electromagnetic field via conversion of electromagnetic energy into thermal energy.

Whereas loss mechanisms occur, a high rate of heating and a high efficiency of energy conversion are expected. The high heating rate represents the key-feature of microwaves heating, because this makes possible to accomplish in short times (seconds or minutes) what would take minutes, or even hours, to be done with conventional heating.

This depends upon slowness of heat delivery rate from the material surface to the core as determined by the differential in temperature from a hot outside to a cool inside. In contrast, use of microwave energy can produce, under some conditions, a bulk heating with the electromagnetic field interacting with the material as a whole. With reference to energy saving, thermal treatments performed by microwave heating can be seen as intensified operations.

Summary of the advantages of microwave heating is as follows:

i. High heating rate.

ii. High efficiency of energy conversion.

iii. Energy efficient heating.

iv. Clean Heating.

v. Less time in heating thus saving in time as well as energy.

vi. Bulk heating can be done.

Essay # 4. Laser Beam Welding (LBW):

Laser beam welding is a welding technique used to join multiple pieces of metal through the use of a laser. The beam provides a concentrated heat source, allowing for narrow, deep welds and high welding rates. The process is frequently used in high volume applications, such as in the automotive industry.

Like electron beam welding (EBW), laser beam welding has high power density (on the order of 1 MW/cm²) resulting in small heat-affected zones and high heating and cooling rates. The spot size of the laser can vary between 0.2 mm and 13 mm, though only smaller sizes are used for welding.

The depth of penetration is proportional to the amount of power supplied, but is also dependent on the location of the focal point: penetration is maximized when the focal point is slightly below the surface of the work piece

A continuous or pulsed laser beam may be used depending upon the application. Millisecond-long pulses are used to weld thin materials such as razor blades while continuous laser systems are employed for deep welds.

LBW is a versatile process, capable of welding carbon steels, HSLA steels, stainless steel, aluminium, and titanium. Due to high cooling rates, cracking is a concern when welding high-carbon steels. The weld quality is high, similar to that of electron beam welding.

The speed of welding is proportional to the amount of power supplied but also depends on the type and thickness of the work pieces. The high power capability of gas lasers make them especially suitable for high volume applications. LBW is particularly dominant in the automotive industry.

Some of the advantages of LBW in comparison to EBW are as follows:

i. The laser beam can be transmitted through air rather than requiring a vacuum,

ii. The process is easily automated with robotic machinery,

iii. X-rays are not generated, and

iv. LBW results in higher quality welds.

A derivative of LBW, laser-hybrid welding, combines the laser of LBW with an arc welding method such as gas metal arc welding. This combination allows for greater positioning flexibility, since GMAW supplies molten metal to fill the joint, and due to the use of a laser, increases the welding speed over what is normally possible with GMAW. Weld quality tends to be higher as well, since the potential for undercutting is reduced.

Lase beam can also be used for polymer weld due to following advantages:

i. Tools and moulds are returned to mint condition.

ii. On-site repairs, minimal post-processing.

iii. Reduced down times.

iv. Welding of wires with diameters as small as 100 microns.

v. Processing of difficult geometries.

vi. Low heat input.

vii. Low risk of distortion, crack formation or softening.

viii. Processing of high-alloy tool steel.

ix. Dissimilar materials joint.

x. Energy efficient process.

Essay # 5. Electron Beam Welding:

Electron beam welding (EBW) is a fusion welding process in which a beam of high-velocity electrons is applied to two materials to be joined. The work pieces melt and flow together as the kinetic energy of the electrons is transformed into heat upon impact. EBW is often performed under vacuum conditions to prevent dissipation of the electron beam. It was developed by the German physicist Karl-Heinz Steigerwald.

Free electrons in vacuum can be accelerated, with their orbits controlled by electric and magnetic fields. In this way narrow beams of electrons carrying high kinetic energy can be formed, which upon collision with atoms in solids transform their kinetic energy into heat.

Electron beam welding provides excellent welding conditions because it involves:

i. Strong electric fields, which can accelerate electrons to a very high speed. Thus, the electron beam can carry high power, equal to the product of beam current and accelerating voltage. By increasing the beam current and the accelerating voltage, the beam power can be increased to practically any desired value.

ii. Using magnetic lenses, by which the beam can be shaped into a narrow cone and focused to a very small diameter. This allows for a very high surface power density on the surface to be welded.

iii. Shallow penetration depths in the order of hundredths of a millimetre.

The effectiveness of the electron beam depends on many factors. The most important are the physical properties of the materials to be welded, especially the ease with which they can be melted or vaporize under low-pressure conditions.

As a source of electrons for electron beam welders, the material must fulfill certain requirements:

i. To achieve high power density in the beam, the emission current density [A/mm ], hence the working temperature, should be as high as possible,

ii. To keep evaporation in vacuum low, the material must have a low enough vapour pressure at the working temperature.

iii. The emitter must be mechanically stable, not chemically sensitive to gases present in the vacuum atmosphere (like oxygen and water vapour), easily available, etc.

Electron beam welding equipment:

Specifically, the equipment comprises of:

1. Electron gun, generating the electron beam,

2. Working chamber, mostly evacuated to “low” or “high” vacuum,

3. Work piece manipulator (positioning mechanism), and

4. Supply and control/monitoring electronics.

Applications of EBW:

Electron beam welding (EBW) is used mainly for fabricating structures that have stringent quality, strength, and joint reliability requirements. For more than 45 years this process has been applied in aerospace, shipbuilding, and instrument manufacturing.

Advantages of EBW:

Compared with arc welding processes, EBW improves joint strength 15 percent to 25 percent. It has a narrow heat-affected zone (HAZ), which results in lighter-weight products. Geometric shapes and dimensions are highly stable, particularly when it is used as a finish operation. It eliminates oxide and tungsten inclusions and removes impurities. The weld metal has a fine crystalline structure.

EBW also is suitable for a variety of difficult applications, such as welding structures on which the reverse side of the butt is inaccessible; gravity welding of thin metal; and welding in various spatial positions. EBW provides a low level of overall heating of the structures; and has the ability to vaccumize the inner volume simultaneously, which is suitable for sealing instruments.

Because EBW is an automated process, the welded joint quality is consistent. The process does not require shielding gases, tungsten electrodes, or edge preparation for welding thick metal. Finally, it can be used to weld some joints that cannot be made by other welding processes.

EBW limitations:

i. High equipment cost.

ii. Work chamber size constraints.

iii. Time delay when welding in vacuum.

iv. High weld preparation costs.

v. X-rays produced during welding.

vi. Rapid solidification rates can cause cracking in some materials.

Apart from the expensiveness of the equipment that is necessary as well as the professional personnel, Electron beam welding responds with high quality results. And can be used with all kind of steel, aluminium, magnesium, copper, nickel, Cobalt alloys as well as with dissimilar materials.

Essay # 6. Process Automation:

Process automation can contribute in many ways to higher energy efficiency in industrial production facilities. Its equipment and systems which ensure intelligent measurement and control of production processes can make a big contribution towards greater energy efficiency. This can result in average energy savings of 10-15% – upto 70% in some cases – in industries using the technology.

Modern process automation solutions can help companies to substantially reduce energy consumption. In the medium to long term, this cuts the production costs for companies using the technology and makes them more competitive. Sectors like metal production, the cement industry, basic chemicals and paper and cellulose are extremely energy-intensive.

An intelligent use of energy becomes the key criterion for corporate success. Energy costs account for approx. 20% of the production costs of complex chemical facilities. In the metal-producing sectors (steel, copper, aluminium), energy costs can be up to 50% of the production costs.

There is enormous potential for energy saving in the use of new products, systems and solutions offered by process automation technology. In order to develop it, it is necessary to optimise all the production-related processes and operations in energy terms.

Here, a distinction is basically made between two key measures:

i. Measures to optimise the technical infrastructure of a production process.

ii. Measures to optimise the actual production process itself.

When optimising the technical infrastructure, there are three main areas which help to prevent additional energy being consumed by equipment failure and resulting start-up and closing-down processes or faulty output. The assessment of the present situation serves to recognise causes of faults and weak points in good time before equipment failure and damage occurs.

The relevant maintenance and repair work is optimally planned and is carried out with minimal impact on the production process. The experience gained from the main areas mentioned above can be used to pinpoint the weak points of plant and to remove them by optimising the infrastructure, thereby substantially reducing the failure rate.

Three main areas can also be identified when it comes to optimising the production process. The first area is process information. Here, it is necessary to ensure that the parameters best suited to the assessment of the process are being measured and monitored with the necessary degree of precision.

Here, the selection of the ‘correct’ yardstick for the evaluation of the process can have a key influence on the amount of energy used. If the process is to be designed well, the best suited aggregates and processes need to be used for the relevant task. An optimally designed facility can be further improved by suitable process management.

Here, all available process information is subjected to a holistic evaluation in context, and the optimal strategy to attain the economic objective is drawn up. This process is frequently supported by the use of computer simulations. Intelligent applications and solutions for process automation can be used to provide the vital information for successful energy management by the companies.

The measurement and analytical equipment and the computer programmes show not only how a facility works: they also simulate different operating conditions. This makes it possible to find the appropriate strategy for an optimal operation of the facility in terms of energy consumption. The software used for this can learn, it can shorten response times, predict trends and optimise maintenance intervals.