Waste Heat Recovery System Engineering Essay

Waste heat recovery system is the procedure of using waste heat that is being produced in assorted warming procedures. There is tremendous heat that is being wasted by industries which affects the efficiency of the industry to a greater extent than any other factors. So, there is an inevitable demand to work out this job and do certain that the efficiency of the industry is increased.

High temperature heat recovery potency is available in many industries. High temperature waste heat available can be utilized for bring forthing power, heating H2O & A ; air, increasing procedure temperature etc. Sing the acute deficit of power, this ready beginning can turn out a blessing to the industry in more than one manner.

This undertaking is carried out at Nava Bharat Ventures Limited ( NBVL ) , Paloncha, and Khammam District in use of waste heat available from Submerged Electric Arc Furnace ( SEAF ) fuel gases by put ining a Double base on balls heat money changer ( LPHX – Low Pressure Heat Exchanger and HPHX – High Pressure Heat Exchanger ) in fuel gas way. By and large Main Condensate & A ; Feed Water in Power Plant is heated in LP & A ; HP warmers of Turbine regeneration rhythm by pulling steam from Steam Turbine extractions.

In this undertaking, Main Condensate & A ; Feed Water will be heated in installed heat money changer by partially/completely short-circuiting LP & A ; HP warmers. Therefore, the steam draw from Turbine extractions will come down/zero. As a consequence, the specific steam ingestion of turbine will besides come down and accordingly the overall efficiency of the whole system is improved.

Chapter 1: Introduction

Waste heat is heat which is generated in a procedure by fuel burning or chemical reaction, and so “ dumped ” into the environment even though it could still be reused for some utile and economic intent. The indispensable quality of heat is non the sum but instead its “ value ” . The scheme of how to retrieve this heat depends in portion on the temperature of the waste heat gases and the economic sciences involved.

Large measure of hot fuel gases is generated from Boilers, Kilns, Ovens and Furnaces. If some of this waste heat can be recovered, a considerable sum of primary fuel can be saved. The energy lost in waste gases can non be recovered wholly. However, much of the heat could be recovered and loss minimized.

Heat Losses -Quality

Depending upon the type of procedure, waste heat can be recovered at virtually any temperature from that of chilled chilling H2O to high temperature waste gases from an industrial furnace or kiln. Normally the higher the temperature, the higher the quality and the more cost effectual is the heat recovery. In any survey of waste heat recovery, it is perfectly necessary that there should be some usage for the cured heat. Typical illustrations of usage would be preheating of burning air, infinite warming, or pre-heating boiler provender H2O or procedure H2O. With high temperature heat recovery, a cascade system of waste heat recovery may be practiced to guarantee that the maximal sum of heat is recovered at the highest potency. An illustration of this technique of waste heat recovery would be where the high temperature phase was used for air pre-heating and the low temperature phase used for procedure provender H2O warming or steam elevation.

Heat Losses – Measure

In any heat recovery state of affairs it is indispensable to cognize the sum of heat recoverable and besides how it can be used.

The sum of heat recoverable can be calculated as, Q = V x I? x Cp x I”T

Where,

Q is the heat content in kCal

V is the flow rate of the substance in m3/hr

I? is denseness of the fuel gas in kg/m3

Cp is the specific heat of the substance in kCal/kg oC

I”T is the temperature difference in oC

Development of a WHRS

Understanding the procedure is indispensable for development of Waste Heat Recovery system. This can be accomplished by reexamining the procedure flow sheets, layout diagrams, shrieking isometrics, electrical and instrumentality overseas telegram ducting etc. Detail reappraisal of these paperss will assist in identifying:

a ) Beginnings and utilizations of waste heat

B ) Upset conditions happening in the works due to heat recovery

degree Celsius ) Availability of infinite

vitamin D ) Any other restraint, such as dew point happening in an equipments etc.

After placing beginning of waste heat and the possible usage of it, the following measure is to choose suited heat recovery system and equipments to retrieve and use the same. ( Reay, 1979 )

The basic technique of the waste heat recovery is to capture the waste heat steams and, using a heat money changer, transportation that heat to another medium to set back into the procedure. The advantages of waste heat recovery are it can cut down installation ‘s one-year fuel measures, cut down works emanations and better productiveness. In procedure warming, utilizing waste heat will displace a part of the fuel or electricity that would otherwise be purchased. Waste heat recovery is ever a good thought when:

The temperature of the waste heat is hotter than the input demands of the procedure.

The fuel nest eggs achieved are greater than the capital and operational costs of the waste heat recovery equipment.

The value of the waste heat steam is determined chiefly by its temperature. It is widely held that any waste heat watercourse ( air or liquid ) of at least 500oF ( 260oC ) is a feasible beginning for recovery. Obviously, the higher the temperature, the higher the quality or value of the waste steam. Harmonizing to a recent Department of Energy ( DOE ) study, with stack temperatures of 1,000oF ( 538oC ) , the heat carried off is likely to be the individual biggest loss in the procedure. Above 1,800oF ( 982oC ) , stack losingss will devour at least 50 per centum of the entire fuel input to the procedure.

Equipment used for waste heat recovery:

The assortment of equipment available for waste heat recovery includes recuperators, regenerators and waste heat and fumes gas boilers/steam generators. The heat recovery procedure can be gas to gas or gas to liquid. The merchandise of waste heat recovery can be preheated burning air, hot H2O and steam. The hot H2O and steam can be used for works services or as portion of the original procedure warming. The steam can besides be used to run steam turbines for mechanical work or to bring forth electricity.

A recuperator is a gas-to-gas heat money changer placed on the stack of the oven or fumes of a premier mover. Recuperator ‘s transportation heat from the surpassing gas to incoming burning air without leting steams to blend. There are many designs for recuperators, but all rely on tubings or home bases to reassign heat. They are the most widely used waste heat recovery devices.A

A regenerator is fundamentally a rechargeable storage device for heat. They can work with gas-to-gas, gas-to-liquid or liquid-to-liquid waste heat beginnings and can be installed on ovens, premier movers, chemical reactors and with steam condensate. A regenerator is an insulated container filled with stuff capable of absorbing and hive awaying big sums of thermic energy. During the first portion of the rhythm, the waste watercourse flows through the regenerator, heating the storage medium. The 2nd portion of the rhythm has the un-heated watercourse flow through the regenerator, absorbing heat from the medium before it enters the procedure. The rhythm so repeats itself. In uninterrupted procedures, two regenerators are required. As with recuperators, there are many designs for regenerators such as heat wheels, inactive, fin-tube and shell-and-tube.A

Waste heat and fumes gas boilers/steam generators are similar to conventional boilers except they are heated by the waste heat steam from the procedure or premier mover instead than from their ain burner. Waste heat boilers are of most value to treat industries that require big sums of steam in their procedure. The steam generated from a waste heat steam will non by and large replace bing boilers but will supplement the steam that they produce, thereby cut downing the energy cost to run the direct-fired boilers. As the steam from a waste heat steam is available merely when the procedure is running, waste heat boilers are by and large designed to run with bing boilers or with steam generators in a combination system. ( Kessler, 2004 )

Chapter 2: Literature Reappraisal

Waste heat may or may non be recovered from all the industries. This fundamentally depends upon the sum of waste heat available in that peculiar industry and the economic sciences involved in its extraction. The heat recovery that is done in some of the industries in India is discussed below.

Cement industry:

India, being the 2nd largest cement manufacturer in the universe after China with a entire capacity of 151.2 Million Tons ( MT ) , has got a immense cement industry.

In cement workss about 40 per centum of the entire heat input is rejected as waste heat from issue gases of preheated and grate ice chest. This waste heat can be efficaciously utilized for electric power coevals. Cogeneration of power besides extenuating the job of power deficit besides helps in energy preservation every bit good as cut downing green house gas emanations.

Cogeneration systems have been successfully runing in cement workss in India, China and South-east Asiatic states. In bing programs cogeneration engineerings based on bottoming rhythms have possible to bring forth up to 25-30 per centum of the power demand of a works. However, the Indian cement industry is yet to do strong attempts in this way due to existence of assorted proficient and fiscal restraints. ( Gulf Coast Clean Energy Application centre, 2008 )

Sulphuric acid Plant:

Sulphuric acid required for a sulphonation reaction is produced in-house utilizing elemental sulfur as the get downing natural stuff. The procedure engineering used for the intent is Double Contact Double Absorption ( DCDA ) procedure. DCDA is considered to be the most efficient procedure engineering ( taking to practically about zero atmospheric emanation of sulfur bearing gases ) for bring forthing sulfuric acid. In the procedure of production of sulfuric acid utilizing elemental sulfur as the get downing stuff hot gas and hot acid watercourses get generated during assorted phases of the procedure. As a portion of the procedure, traditionally the heat contained in the hot gas watercourse is recovered in the signifier of steam in waste heat boiler. The waste heat in the hot acid steams is low class heat ( temperatures being low ) and is non recovered in all the traditional sulfuric acid workss. The extent of recovery of waste heat from the hot fluid steams, and the quantum of steam generated depends on the proficient characteristics of the procedure works, the capital cost involved in the procedure of heat recovery and the chance to utilize the cured heat. ( Prakash, 2008 )

Waste heat is being bigger than solar energy:

The typical industrial power works in the U.S. is merely approximately half as energy efficient as those used in 1910, harmonizing to Sean Casten, CEO ofA Recycled Energy Development ( RED )

In fact, the 1s Thomas Edison designed were more efficient. Edison ‘s workss were n’t really really efficient as doing electric power, Casten noted, but he sold the heat generated during operations, which boosted the overall. A full two-thirds of the fuel burned to bring forth power in today ‘s power workss – which for the most portion were built in the mid-1960s with 1850s engineering – gets lost he asserts.

Although it can be slippery and expensive to tackle, waste heat is acquiring increased focal point as a beginning of power in both the U.S. and China, largely because of the measures of heat out at that place. A survey conducted by Lawrence Berkeley National Labs estimated in 2005 that the U.S. entirely has 100 gig Watts of untapped electrical capacity in the signifier of waste heat that yearly could bring forth 742 terawatt hours of power. That ‘s bigger than the solar fleet, which gets measured in megawatts. UC Berkeley ‘s Arun Majumdar estimates that the U.S. consumes 100 quads ( 100 quadrillion BTUs ) of energy a twelvemonth and 55 to 60 per centum of it gets dissipated as waste heat.

Generating that heat, of course, besides means extra nursery gases. Approximately 42 per centum of C dioxide emissions come from power workss, said Casten. If power workss are genuinely merely 33 per centum efficient, that means that 28 per centum of the C dioxide end product in the U.S. could be eliminated without pinching the national life style. Cars merely history for 19 per centum.

Some companies, such asA Cypress SemiconductorA and GMZ Energy, are seeking to develop thermoelectric stuffs. These are semiconducting materials that, wrapped around a steam pipe, could change over ambient heat to electricity.

Companies like Israel ‘s Ormat and Westmont Ill.-based RED – which raised a $ 1.5 billion fund with Denham Capital Management to take on waste heat undertakings – are mostly concentrating on the more traditional techniques. Namely, exploit extra steam force per unit area and heat to turn a turbine, power heating systems or boil more H2O. It all depends on the fortunes on the land. Waste fuels can besides be harvested.

While the majority of waste heat is generated in big workss, there are besides smaller pockets. Natural gas grapevines are equipped with supporter Stationss which maintain the force per unit area inside the grapevine as the gas travels from one point to another. Each one on norm requires 10 megawatts of power but gives off about 3 megawatts worth of waste heat.A

“ There are chances all over the topographic point – Si makers, cement, steel, ” he said. “ They have high volumes of reasonably high quality waste heat. ”

One of the company ‘s more dramatic undertakings will travel online in 2010. West Virginia Alloys, a Si maker, will put in a waste heat recovery system that will bring forth 45 megawatts of electrical power. The company merely uses 120 megawatts right now. ( Put another manner, the company merely truly needs 75 megawatts for its operations and is presently firing off 45 megawatts. )

To day of the month, the large challenge has been cost. Most industrial-scale waste heat undertakings cost between $ 5 and $ 50 million. That ‘s excessively high for most to pay out of capital budgets and excessively low for a public funding undertaking.

“ There ‘s a immense Goldilocks job, ” he said. To acquire around this, RED pays for any waste heat recovery system it installs and so gets paid for energy nest eggs under long-run contracts. Goldilocks job is nil but happening the appropriate solution for the job. ( Kanellos, 2009 )

Hence holding looked at batch of illustrations and the yesteryear and the nowadays of waste heat recovery, we can entree that waste heat is non recovered in all the industries. It depends on the assorted factors as the sum of heat, the economic sciences involved and the feasibleness of the waste heat to change over into utile heat in that peculiar works. The works that I have looked at has that chance to change over waste heat into utile heat in all the positions.

Chapter 3: Methodology

Nava Bharat Ventures Limited has Electrical discharge furnaces for production of Ferro alloys ( Manganese, Silicon and Chromium alloys ) , which are indispensable inputs for industry of steel. Manganese and Silicon alloys impart strength and hardness and act as powerful deoxidising agents, Chromium alloys do steel corrosion resistant and heat resistant.

The smoke from the furnace is diluted with ambient air and cleaned by the gas cleansing works before exhausted to atmosphere. One of the furnaces is equipped with beaming gas ice chest. It is intended to salvage the heat, which is dissipated from the beaming ice chest. It is proposed to put in a dual base on balls heat money changer ( LPHX-low force per unit area heat money changer and HPHX-high force per unit area heat money changer ) , that transfer the waste heat to Main condensate and provender H2O before the chief condensate and provender H2O are preheated in the LP & A ; HP warmers of 32MW Captive Power Plant.

Chapter 4: Findingss

Ferro Alloy Plant agreement:

The works consists of the Submerged Electric Arc Furnace ( SEAF ) , Bag filter, Radiant Gas Cooler, ID fan and Stack.

The submersed discharge furnace is a semi unfastened furnace with a capacity of 27.6 MVA, in which the ores are melted. The off gas is emitted from the furnace. The measure of the gas varies depending on the natural stuff. The dilution air is drawn from the gaps around the furnace by the attempt from ID fan, which is located at the downstream of the radiant gas ice chest.

There are two chimneys straight connected to water-cooled furnace goon. These two chimneys are provided with butter fly dampers, which are usually kept under closed status. Each chimney is provided with the subdivision connexion to radiant gas ice chest below the butter fly dampers. Under normal fortunes the gas goes through the radiant gas ice chest.

Radiant gas ice chest is an agreement of gas transporting pipes. The heat from the gas is cooled by the natural radiation and convection to ambient air.

The gas after chilling is drawn by the ID fan and sent to the bag house to take the dust in the gas watercourse. The bag house is provided with rearward air fan to clean the dusty bags. The bag house is with eight compartments out of which one compartment will be under cleaning at any clip. The bag stuff is fibreglass.

Manufacturing Procedure:

The above metal, known as majority Ferro alloys, are manufactured by bear downing pre-determined measures of natural stuffs dwelling of ores, reducing agents and fluxes into submerged electric discharge furnaces. The mix of natural stuffs depends on the specification of Ferro metal to be produced.

High currents at low electromotive force are passed through the three electrodes of the furnace and the charge of natural stuffs. The opposition offered by the natural stuffs to the flow of electricity creates immense heat, ensuing in smelting of the natural stuffs charged into the furnace and the attendant metallurgical reactions takes topographic point.

Carbon in the reductant reacts with the oxides in the ores. The metallic content of the ore forms a Ferro metal while the other gangue stuffs become scoria. Both the Ferro metal and the scoria are in liquid signifier because of the high temperature in the furnace bath. Due to difference in densenesss the metal and scoria are separated. The denseness of scoria is lower than the liquid metal, scoria floats to the top.

At periodic intervals, the molten metal and scoria are tapped out from the furnace bath through a tap hole. The liquid scoria is granulated by encroachment against a jet of H2O in instance of Ferro chrome and Silico Manganese. The Ferro Manganese scoria is reused for the production of Silico Manganese due to its high Manganese and low Phosphorous content.

The granulated scoria is used for industry of fly ash bricks and concrete rings.

The liquid metal ( i.e. , the Ferro metal produced ) is collected in a ladle and dramatis personae into molds in a uninterrupted casting machine or pulverization beds as a bar. These bars, after chilling, are broken down to the size specified by the client, depending on the metallurgical patterns followed by the client. The sized stuff is packed in bags of 50 kgs for domestic markets and one tone or free for export markets in general and dispatched to the clients.

Thermal Power Plant agreement:

Thermal Power Plant chiefly consists of Boiler, ESP ( electrostatic precipitator ) , Steam Turbine, Generator, Condenser, LP warmer, HP warmer, Boiler Feed Pump, Condensate Extraction Pump, Deaerator, Cooling Tower, CW ( clockwise ) & A ; ACW ( anticlockwise ) pumps, Water intervention works, Coal and ash handling works.

Procedure of Power Generation:

The Thermal Power Plant employs steam turbine based power coevals, which is the most widely used method for production of electricity from coal. In this system, H2O is used as a working fluid and is heated in a Boiler by firing coal, to bring forth steam, which, on farther warming, becomes superheated steam holding a high temperature of 530OC and a high force per unit area of 93 kg/cm2. This superheated steam runs the turbine, which converts heat energy into mechanical energy and drives an electrical generator coupled to it. The generator converts the mechanical energy into electric power.

The subsidiary system includes go arounding H2O system, ash aggregation and ash handling system, coal handling system, electrical switchgear, transformers, etc.

The needed coal is crushed and screened in the Coal Handling Plant with the aid of crushers & A ; screens. This crushed coal is transported to boiler sand traps through conveyers. From the sand traps, the coal is fed into the boiler furnace.

Necessary air for burning is pumped into the furnace by Primary and secondary air fans. Primary and Secondary air are heated in Air Pre-Heater by using waste heat in fuel gases before Federal to furnace for bettering the Boiler efficiency and the fuel gases are exhausted to atmosphere through ESP & A ; Chimney.

Ash collected after burning of coal in two different locations. One is under bed and the other is at ESP. Ash collected under bed is called as underside ash or bed ash, which is conveyed to ash pool through slurry system and Fly ash at ESP is conveyed pneumatically to ash storage silo.

Required feed H2O in Boiler for steam coevals is pumped from H2O intervention works with the aid of Boiler Feed Pump.

The steam turbine is a wholly condensing type. After go throughing through the turbine, the steam is condensed to H2O in the capacitor and pumped back to the boiler. This rhythm is repeated. There are no discharges from this system except a really minor measure of steam blown out of the steam circuit to keep the proficient quality of boiler provender H2O.

The steam Turbine has three extractions, one is for HP warmer to heat the provender H2O, second is for Deaerator to deaeration procedure and 3rd is for LP warmer to heat the chief condensate.

The chilling H2O system for distilling the steam is of go arounding type. From the chilling tower sump, cool H2O is pumped to the turbine capacitor where it picks up heat while distilling the steam and is pumped back to the chilling tower for chilling.

Waste Heat Recovery System

The company ( NBV ) has installed a heat money changer to use the heat available in the furnace fuel gases, for heating the boiler provender H2O and chief condensate of 32 MW Captive Power Plant located in the same premises. The heat money changer is of cross flow type with two base on ballss. The first base on balls is called as HPHX and the 2nd base on balls is called as LPHX. The fuel gases are passed vertically downwards over packages of horizontal H2O tubings in HPHX and upwards in LPHX. Feed H2O and chief condensate are heated in HPHX and LPHX severally. The flue gas coming from the furnace passes over HPHX foremost, subsequently over LPHX and eventually enters Gas Cleaning Plant ( GCP ) through an ID fan.

WHRS is meant for using the waste heat available in Submerged Electric Arc Furnace ( SEAF ) fuel gases. It is installed in the down steam of furnace. This system consists of Low Pressure Heat Exchanger ( LPHX ) and High Pressure Heat Exchanger ( HPHX ) to heat the chief

Condensate and feed H2O.

Constructional Features:

WHRS chiefly consists of ducting from SEA furnace to heat money changer, dual base on balls Heat money changer, Ducting from Heat money changer to GCP ID fan, Feed H2O & A ; Main condensate lines from Power Plant.

Ducting from furnace to Heat money changer: Submerged Electric Arc Furnace ( SEAF ) is holding two chimneys of diameter 2000mm each with 65Mtrs tallness. A pat off ( size 2000mm ) diameter from each chimney is taken horizontally at ( + ) 26.50Mtr lift and made a common canal. After tapes, pneumatic operated isolation dampers are provided in two chimneys. The other terminal of common canal is connected to inlet of Heat money changer. The diameter of common canal is 3000mm. One dilution damper of size 800mm is arranged in common canal to thin the fluke gas with fresh air.

Double base on balls Heat money changer: It is a two – base on balls cross flow type heat money changer. First base on balls is called High Pressure Heat Exchanger ( HPHX ) and the 2nd base on balls is called Low Pressure Heat Exchanger ( LPHX ) . HPHX & A ; LPHX consists of 3 faculties each and holding H2O tubing spirals inside the shell. Fuel gases are go throughing over the H2O tubing spirals during operation. A by-pass canal ( 1000mm diameter ) with modulating isolation damper is provided in between HPHX & A ; LPHX. Insulation stuff of 175 & A ; 125mm midst is provided on HPHX & A ; LPHX severally.

Ducting from Heat money changer to GCP ID Fan: It is 2200mm diameter. LPHX beltway canal is connected to the mercantile establishment canal. Outlet canal is provided with one temperature sender & A ; one bill of exchange sender. The ID fan recess is holding a multi lower damper for commanding the flow rate.

Feed Water line: A tap – off is taken from Power Plant feed H2O line after HP warmer with a motor operated isolation valve ( with beltway valve ) and connected to HPHX. The mercantile establishment from HPHX is connected before the control valve in Power Plant feed H2O line with a motor operated isolation valve. One HPHX by-pass motor operated valve is provided near control valve. Insulation stuff of 75mm midst is provided over the complete piping.

Main Condensate line: A tap – off is taken from Main Condensate line of Power Plant after LP warmer with a motor operated isolation valve ( with beltway valve ) and connected to LPHX. The mercantile establishment from LPHX is connected before the control valve in Power Plant Main Condensate line with a motor operated isolation valve. One LPHX beltway motor operated valve is provided near control valve. Insulation stuff of 50mm midst is provided over the complete piping.

Procedure:

Feed H2O coming from the Boiler Feed Pump with a temperature of 155OC is heated in HPHX with 380OC of fuel gas coming out from SEA furnace, so the provender H2O temperature increases to 225OC and the fuel gas temperature comes down to 226OC. This feed H2O line is connected to the Boiler for steam coevals.

Main Condensate coming from Condensate Extraction Pump through Steam Jet Ejector & A ; Gland Steam Condenser with a temperature of 89OC is heated in LPHX with a 226OC of fuel gas, so the Main Condensate temperature will lift up to 123OC and the fluke gas temperature will comes down to 160OC. This mercantile establishment of Main Condensate is connected to Deaerator recess piping.

The fluke gases are discharged to atmosphere, after using the waste heat available in flue gases through chimney with the aid of ID fan.

The extraction steam for HP & A ; LP warmers will be cut off from Turbine i.e. HP & A ; LP warmers are bypassed, while Waste Heat Recovery System is in service.

Chapter 5: Decision

The aim of this undertaking was to plan a Waste Heat Recovery System ( WHRS ) for Nava Bharat Ventures Limited. The bing system was examined and found 1.25 ten 107 kCal/hr of waste energy is reject to the environment from Sub – merged Electric Arc Furnace ( SEAF ) .

Different methods of heat recovery were examined to find which are most executable with the NBVL. It is necessary to measure the selected waste heat recovery system on the footing of fiscal analysis such as investing, depreciation, payback period, rate of return etc. In add-on the advice of experient advisers and providers must be obtained for rational determination.

When ciphering energy nest eggs and payback periods for heat recovery units, it is of import to compare heat recovery with the current beginning of energy for bring forthing thermic energy, which may be a low-price dodo fuel such as natural gas.

The purpose of put ining a new energy recovery system at Nava Bharat Ventures Ltd was to be able to cut down fuel cost and increase Steam Turbine heat rate caused by heat being lost to the environment. Simultaneously, the GDP ID fan power ingestion will cut down, life of GCP bags is increased by cut downing the gas temperature at GCP recess and thermic pollution besides will cut down.

A Double base on balls Heat money changer was selected and designed to retrieve heat from issue fuel gases of SEAF system and heat the Feed Water and Main Condensate by using the waste energy available in fuel gas.

The chief focal point of this undertaking was to cut down the cost of energy measures by cut downing the sum of fuel used to heat the installation.