Energy savings

Our full support to our customers is reflected in the main idea and trend of our work. There we put emphasis on cutting power consumption and energy saving and looking for a new construction solutions with maximum satisfaction for our customers needs. We achieve that with permanent control of technical trends and with active work on our own research.

 

Author of information bellow is ing. Josef Fík

ECONOMICAL OPERATION OF UNDUSTRIAL GAS APPLIANCE

 

In industrial gas appliance there are heat-treated products from the metallurgy and mechanical engineering field moreover from glass and ceramic field and many others:

 

- steel products, cast stocks, engineering steel, metal sheets, wires

- products of non ferrous metals (aluminium, copper, brass)

- utilitarian and packaging glass, laboratory and flat glass…

- products for building industries (lime, cement, bricks, roofing, etc.)

- utilitarian and sanitary ceramics, artistic ceramics, tiles, fireproof materials

- oil industry products, commodities for colour production

 

Industrial appliance help in other field of production:

 

- grocery production ( bakery ovens, storage kilns, brewery, nut and coffee roasters)

- production of illuminators

- textile production ( fabric glowing)

 

 

1. Basic types of industrial appeances

 

a) engineering and metallurgy

 

• heating furnace ( push furnace, walking beam furnace, pit furnace, car-type furnace, carrousel furnace)
• furnaces for metal heat-treating
• melting furnaces for non ferrous metallurgy (aluminium, brass copper, bronze, etc.)
• furnaces for drying of fire sand, forms and piths
• furnaces for steel chemical treatment (cementing, nitration)
• protecting and controlled atmosphere developers from gaseous fuel
• reactor preheating auxiliary ( preheating steel constructions before welding, furnace ladle preheating in foundry, preheating of smith impression die, etc.)

 

The picture shows industrial gas furnace for preheating and heat-treating of steel products

 

 

 

b) Ceramic industry

 

• tunnel furnaces for tile, pottery, utilitarian and sanitary ceramic burning.
• batch furnaces for earthenware burning
• furnaces for electrical porcelain burning (dice-insulators, plugs)
• furnaces for fireproof material burning ( fire-clay, dinas, corundum, normal and adapting pipes)
• furnaces for graphite products burning
• batch furnaces for artistic ceramics burning
• furnaces for dental material burning etc.

 

On the picture is batch furnace for utilitarian pottery burning

 

 

 

c) glass industry

 

- melting bath and pot furnaces

- cooling batch, conveyer (utilitarian glass) and roller hearth furnaces (flat glass) furnaces

- glory hole furnaces for handmade glass products

- engines for spectacle glass

- automatic for glass bricks

- device for laboratory sillicic glass production

- burners for flame cutting and burning goblet, glass and oven glassware edges

 

d) Construction industry

 

- shaft furnace for lime burning

- rotary furnace for cement production

- facility for drying of facade rendering

- Hoffman kiln (annular kiln) for brick burning etc.

 

e) Chemical industry

 

- chemical bath heating

- fluid kilns

- high pressure autoclaves

- melting barrels

- sulfonators

 

f) Grocery industry

 

- conveyer furnaces for bread baking

- extracting steam furnace

- drying kilns for cocoa beans

- storage dryers and caramel malt roasters

- nut and coffee roasters

- brewery

 

g) Bulb, vacuum and fluorescent tube production

 

- bulb automatic machine

- furnaces for fluorescent tube production

- automatic machine for vacuum tube sealing

 

h) Agriculture

 

- grain drying installation

- oven granulating

- heating for greenhouses

 

i) Textile production

 

- burners for fabric and yarn burning

- rollers burning for fabric print

 

j) Waste incineration plant

 

- furnaces for municipal waste

- furnaces for hospital waste

- high temperature furnaces for pollutant substances

 

In industry is used gas for different technological heating with open flame of gas burners aside from classical gas furnaces. Efficiency of natural gas usage is very low in these types of heating as the flame of burners radiates into the free space and there is unlimited entry of second air into the flame. Most frequent types of technological heating are:

 

 

• drying and heating of lining in foundry pots before metal casting
• drying of foundry forms
• heating up water and technological bath (for washing machine parts, scalding pigs in slaughter house..)
• flame shutter of continuous furnaces with controlled atmosphere
• railway tire heating before its dismounting
• burning of old gas pipe insulation

 

On the picture is shown heating of foundry pouring pot with gas burner.

 

 

 

2. Gas fuel for heat process in industry

 

 

Gas fuel is mixture of flammable and non-flammable gas which evolves heat during burning with air. They are used for household heat production, for the field of services, industry and heating. There is used natural gas in the Czech republic, which is taken from in-transit pipeline and natural gas taken from Norway. Liquid hydrocarbon gas is less common heat production. Hydrocarbon (propane and butane) generates as a side product of raw oil processing. Massive part of the production goes to households, where is no possibility of natural gas usage. Other gas fuel for industrial companies such as coal mine are natural gas as product of degassing and carboniferous gas. Next gas is coke oven gas which is used in metallurgical production for technological processing in industrial furnaces. This gas generates as a side product of hard coal carbonation in coke oven plant.

 

 

3. Gas burners

 

Gas burner is a device, where chemical energy of gas fuel is turned into heat energy through combusting and then it is used as a heat source for the gas appliances.

 

a) Gas burners with compulsory air supply

 

Gas burners with compulsory air supply make a main group of gas burners and they are mostly used for technological heating in industrial furnaces. These burners usually work with low gas fuel overpressure (P_1p 5 kPa) a and with air burning overpressure of P_1v=1 to 6kPa. The source of air combusting is usually the centrifugal fan. Dividing burners with compulsory air supply into groups depends on the way of mixing the gas fuel with air and on the characteristics of the flame. The basic types are:

 

• parallel double flame burners
• half turbulent burners with mid-sized flame
• turbulent burners with short flame
• pulse burners with high speed of combustion gas
• radiant burners
• radiant tubes with enclave burning

 

Most of the burners which are used for technological heating belong into the group of burners with compulsory air supply, except mid-pressure injector torches. There is typical burner with compulsory air supply shown on the picture.

 

 

b) Injector torches

 

Mid-pressure injector torches (see the picture) are only used for industrial heating, especially for industrial furnaces heating. Mid-pressure injector torches have many advantages compare to burners with compulsory air supply:

 

 

 

Combusting air is sucked into the burner by a gas fuel injection effect so there is no need of installing the fan for combusting the air and the air pipelines. The energy saving for a fan working is generated by the same time and it makes 2% of furnace absorbed heating power.

 

Injector torches have self-regulated ability, which enables a stable combusting ratio when change of burner’s power appears.

 

 

c) Radiant arc tubes

 

Radiant arc tubes are low-pressure gas burners with compulsory air supply, with gas-air mixture combusting in closed tube made of iron or ceramics. Venting goes out of heated space. The most widespread type is jacket radiant arc tube (see the picture) with in-built metallic recuperator, where is heated combusted air by combustion gas going out of the tube. Combusting tube of jacket radiant arc tubes are made of ceramic segments or of re-crystallized silicon carbide. Radiant arc tubes are used for heating industrial furnaces with indirect heating when steel and non ferrous metals are heat-treated in the atmospheres controlled setting, when the isn’t wanted a contact of the batch mixture and combustion gas.

 

 

 

 

d) Pulse burners

 

Pulse burners work in high exit velocity of combusting gas from combusting tunnel vent (80 to 120m.s-1) where is homogenous medium dynamically effected. In the picture there is pulse burner with adapting pipe made of re- crystallized silicon carbide. Burners with this adapting pipe can burn mixture of natural gas and preheated air pu to 600°C in temperature of 2000 °C in combusting tunnel.

 

 

 

 

 

 

 

 

 

 

 

In this picture there is pulse burner with electrical ignition and ionizing control of a flame during the control test.

 

 

 

 

 

 

 

 

 

e) Recuperative burners

 

Recuperated burners are burners with recuperators for Heating up combusting air. They are placed into in-built body of burner. Heating up of combusting air by heat of combusting gas, which leaves working space of furnace is separated into numbers of small but highly effective recuperators, compare to classical recuperators, which centrally heat up for all furnace burners.

 

In the picture there is recuperated burner for heating industrial furnaces, it contains:

 

• gas body with regulating a measuring armatura
• air body with regulating a measuring armaturas
• recuperator
• ejector for combusting gas exhausting
• gas and air jet tubes
• adapting pipe of combusting tunnel
• burning and controlling electrodes

 

 

 

 

 

f) Regenerative burners

 

Regenerative burners work discontinuously compare to recuperative burners which heat up combusting air continuously in constant temperature parameters. Heating and flue systems of the furnaces which are burners equipped is divided into two parts, which are placed on opposite sides of the furnace. They work alternately in the way of taking turn in heating function and combustion gas flue function (see the picture). The changeover cycles in regulated period of time, when the cycling direction of combustion gas is changed. The cycling goes into second part of the second part of regenerative burners. Combustion air cycles through firs part (system), which is heat up to high temperature (800 °C to 1000 °C) and cuts gas fuel consumption as in case of recuperation.

 

 

 

 

 

 

4. Energy savings – heat loss of industrial furnaces

 

Gas furnaces heat loss is a part of heat supplied by combustion of gas fuel which is not effectively used in furnaces.

 

 

 

 

• Heat loss caused by combustion gas, which are leaving working space of appliances Qk

• Heat loss through the appliance’s walls Qs

• Heat loss caused by its storage inside of appliances Qa

• Heat loss caused by heat emission through the appliance’s vents Qo

 

 

 

 

 

 

 

 

In the picture is shown dependence of heat loss - caused by leaving combustion gas - on its temperature.

 

 

Heat loss caused by leaving combustion gas makes the biggest part of heat loss. Part on total furnace loss is much bigger than in case of other gas appliances and it reaches 70% of total amount of heat given to furnace compare to 10% - 15% in case of other gas boilers. This huge difference is caused by high temperature in furnace’s working space. High temperature is needed for technological processing (steel melting, ceramic burning, steel heating up before its shaping, etc.) and that means that leaving combustion gas has got high temperature too.

 

 

 

 

 

 

 

 

Industrial furnace efficiency

 

Power efficiency of industrial furnace is determined by formula:

 

η	Quz	*100%
	QD

 

Quz - amount of heat needed to reach technological qualities of heat-treated product ( kJ.h – 1, kWh)

 

QD – total amount of heat supplied by gas fuel combusting

 

 

In table 1 there are mentioned average qualities of older industrial gas furnaces, which are still being used.

 

Furnace temperature (technological process)	charge temperature	average efficiency
chamber (steel heating) bogie hearth (steel annealing) curcible melting (Al) bogie hearth drying kiln (send forms)	1150 950 730 450	26 28 30 32

 

 

in table 2 are mentioned average qualities of efficiency of new types industrial gas furnaces with fibrous insulation. These qualities were measured under the working conditions during combusting of natural gas and combustion air which was heated up in recuperators or in regenerators.

 

Furnace temperature (technological process)	charge temperature	combustion air temperature	average efficiency
car-type (steel annealing) chamber (steel heating) car-type (ceramics burning)	950 120 1380	350 600 850	35 45 58

Temperature is in °C and efficiency is in %

 

 

5. Energy saving during the heating process in industry

 

The number of working industrial furnaces has cut down under the influence of metallurgy industry inhibition which has lasted for last few years. There is only half of the original number of 1200 furnaces provided in the Czech republic. Industrial appliances users still don’t operate their industrial facilities economically. Specific heat consumption of industrial furnaces is highly over the top in the Czech republic compare to other countries. It isn’t just because of an old furnace types, which are usually in a bad condition but also the way of operating them and the bad staff qualification. Unfortunately, this condition isn’t improving even the price of energy keeps growing, which should motivate users to cut power consumption and remove and update furnaces.

 

The way of energy savings goes through cutting its heat loss:

 

- recuperation, regeneration

- using the linings and heat insulation with high thermal resistance

- equipping appliances with modern operating systems for thermal mode control

 

The next way of energy saving is operating optimal mode of appliances for each technological processing.

 

 

 

Leaving combustion gas heat usage in industrial furnaces:

 

1 m³ of natural gas of 1200 °C temperature contains 1870 kJ approximately, which is 0,52 kW of heat. The heat which stays after the combustion gas left the working space, can be reused for heating up of combustion air which goes to the furnace burners. That cuts heat delivery to the furnace supplied only by heat from natural gas combusting. In the picture is shown the dependence of natural gas savings (according to the natural gas consumption during its combustion with cold air) on the combustion air and gas temperature when the natural gas burning is multiplied by stoichiometric basis of combustion air n=1,1.

 

 

 

 

Usage of combustion gas heat in gas furnaces is reached by installing “combustion gas – air” changer into the combustion gas outlet. The methods for heating up the combustion air:

 

 

a) Recuperation - continual heating up of combustion air in metal or ceramic recuperators, eventually in recuperated burners.

 

In the picture there is a recuperator made of steel heatproof tubes.

 

 

 

 

 

 

 

In the picture on the left is shown the placing of this recuperator in the furnace.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

In the picture on the right is radiant burner shown. This radiant burner heats up the combustion air for a big rotary-hearth heating furnace with 9 600 kW input. The top temperature of heated air is 600 °C. The gas saving is 40% compare to operating on cold air. (see the picture). The recuperator is 6m of high and the diameter of its radiant part is 2200 mm.

 

Besides the receperators with central heating of combustion air there are recuperative burners used. Their description is shown above.

 

In the last picture shows where recuperative burners are placed in chamber furnace, where they work as fuel gas installation.

 

b) Regeneration - discontinuous heating of combustion air in ceramic regenerators, eventually in regenerative burners (see the picture). Heating and flue system of industrial furnaces, which are regenerative burners equipped is divided into two parts, which are placed on opposite sides of the furnace. They work alternately in the way of taking turn in heating function and combustion gas flue function. Combustion air is heated up to 850 °C in regenerators and regenerative burners, which produces 45% to 50% of gas savings as you cam see on the graph.

 

 

Cutting the heat loss through the appliance walls a)makes 8% to 12% of heat loss given to the industrial furnace. The possibilities of cutting this loss are very small. Only if the loss value becomes higher than above, the wall insulation improvement or changing for a new appliance is the solution. Then the heat loss is stopped by lightened lining materials fibrous insulating materials with high thermal resistance. Unfortunately the costs of a new wall insulation of older furnaces are very high and the investment recovery depends on the size of appliance and its working capacity per year. In case of brand new furnace, there are modern linings and insulation materials automatically used. The lining change in old furnaces as the recuperator or regenerator installing depends on furnace operator’s financial limits and relatively low price of natural gas.

 

Older furnaces with classical lining is wallcovering by fibrous material used. The principal of this solution is in gluing ceramic units onto modified old lining by special lute. The saving goes up to 15% in this case.

 

c) Cutting the heat loss by accumulation in the appliance

 

The accumulation heat loss generates when the furnace mass cools down when the operating is finished or disturbed. This loss is massive in case of appliances with heavy linings and with short operating time (ex. gas furnaces where the heat of walls, lid and hearth vaporises without any use.) Possibilities of cutting this loss are the same as in case of wall heat loss. That means to use lightened insulation materials. These materials have got much better insulating abilities but smaller heat accumulation thanks to lower value of specific thermal capacity. Next possibility of cutting the heat loss is in organising operating mode of the appliance.

 

d) Cutting the heat loss of heat emission through the working holes

 

The heat loss of heat emission through the working holes generates when the working holes (doors, charging hole, observation window etc.) are open during the operating time, ex. when the charge is manipulated.

 

The possibility of cutting such a heat loss is to keep the operating rules.

 

 

e) a)The operating mode optimisation of the industrial appliances

 

Amount of heat loss of gas furnaces depends also on organising its mode

 

- quality of thermal mode operating

- charge structure and the way of its placing into the furnace

- level of furnace cooling between each working cycle

 

 

f) a)The quality of thermal mode operating

 

The thermal modes of furnaces with small technological meaning, without special requirements for heat treatment quality (small smith chamber furnaces for drop and free forged, crucible melting furnaces, drying kilns for foundry sand, forms and piths, glass cooling and glory hole furnace, etc) are mostly manually operated. The staff (smith, glassmakers)doesn’t usually have proper qualification and doesn’t have motivation for economical operating of the thermal mode. The most common deficiencies are:

 

- faulty fixed combustion ratio

- technological temperature overrunning

- permanent appliance operating in maximal input

- opened charged holes

- opened chimney valve when the operating cycle stops

 

The operating deficiency mentioned, which are cause by imperfect thermal mode operating, generate rises specific heat consumption of 30% and rises costs of its servicing and repair.

 

Charge structure and the way of placing it

 

This element is connected with optimal usage of working space has got major influence on specific thermal consumption of big modern furnaces which are automatically operated. It appears in engineering branches with small number of furnaces and big number of products, which are heat treated in these furnaces. For example: annealing of a big and rugged weldments in car-type furnace is specific heat consumption much bigger than if the same amount of massive casts are heat treated. In this case is specific heat consumption can be affected by appropriate charge structure and the way of its placing into wagon.

 

Furnace cooling between each working cycle

 

If there are very long breaks between working cycles (single shift) the heat loss builds up compare to operating with small breaks (multi shift or uninterrupted operating). The lining absorbs the heat. This heat loss can be treated by work organisation.

 

 

6. Controlling systems of industrial gas furnaces

 

The implementation of difficult technological processing, which are effected in industrial gas furnaces, is impossible to work without facilities which control and operate parameters, economical and save furnace functioning. Modern control systems are drawn up as programmable logical controller, which is formed in an operator and procedural section. Operator section perform communicative mediator between furnace operating and control system. The operator panel shows stages of operating, putting in and keeping of technological parameters, displaying and storage of operating and faulty reports about the furnace stage. The service staff have got the minimal effect on operating technological and economical processing. Their responsibility is only to put in the operating data ( choice of temperature curve according to the type of final product and its quality needed). The controlling systems mentioned are very expensive and they are mainly used for special technological processing of steel heat treating and other metal materials with high requirements on quality. The industrial furnaces equipped with modern control systems have positive effects mention above and secondly they cut the energy consumption of 15% to 20% comparing to manual control.

 

desatero hospodárného provozu pro úspory energií:

1. Using the heat of combustion gas to heat up combustion air ( recuperation, regeneration) – in case of gas furnaces which have output more than 500kW and the working space temperature more than 600°C, which were technically and economically analysed.

2.Using heat proof in combination with fibrous materials for the lining, which cut the heat loss through the walls of the furnace and cut the heat loss of periodic (cyclic) furnace by accumulation.

3. Equipping the furnace with appropriate measuring and regulation engineering according to input amount and technological type of the furnace to limit negative effect of operating staff (programmable logical machines, combustion rate regulation.)

4. Choosing the right gas burner types for technological processing while the drafting heating systems. Choosing the right number of burners and their output and their placing into the furnace to reach the best efficiency of charge heating. The combustion gas flow should be organised to maximally use the heat of combustion gas for a charge preheating(mostly continuous furnaces).

5. The operating gas furnaces economy depends on furnaces sucking conditions and on effective pressure regulation in working space. sucking in of derivative air into the working space boosts the heat loss through the combustion gas and thereby natural gas consumption.

6. When the charge is placed, the capacity and appropriate charge structure should be kept.

7. Periodically working furnace has to be organised in the way that the charge is putted in when the furnace is still hot. The chimney valves of gas furnace have to be closed while the working break. The manipulating outlets (the doors, etc.) open only for necessary time limit for putting in the charge. The staff has to be trained in bases of economical operating and motivate them save heat energy.

8. Gas furnace - the regular set up control of the optimal combustion ratio and the function of control ratio to keep the smallest balance of combustion air while the natural gas combustion. To equip the furnace with regulation of combustion ratio according to the temperature of combustion air.

9. To higher technical level of older appliances their modernisation has to be done. There is relatively low cost used for the improving of furnace parameters ( output, efficiency, even temperature, etc.)

10.The regular measuring for counting the balance, which can be used for calculating the appliance efficiency.

When all these principals (codes) are kept the major energy saving and high refund of the costs will satisfy your work.

Ing. Josef Fík

OUR ADVANTAGES

• experience on the field of energy savings
• cooperation with research and test institutions
• experiences in reconstruction and modernisation which can be proved by our references

REFERENCES

In past ten years of our activities se got many of home and international references. There are for example the most interesting on the list: car-type furnace 25 m3 for magnesite burning, many car-type chamber furnaces over 20 m3, special burners and combustion devices, etc.

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