Technology

It is necessary to notice that the completeness of combustion of fuel an insufficient attention is often paid. At an incomplete combustion of a soot particle and not decayed fuel envelop dust particles, thereby increasing windage and worsening hydrophilism that reduces the efficiency of wet dust removal devices. Besides, such particles cause «greasing» of fabric filters, considerably raising their resistance.

Incomplete combustion of fuel can lead to failures in work of the burner and difficulties at its flaming up.

Use for manufacture asphalt-concrete dust mixes at presence in it of products of incomplete fuel combustion can negatively be reflected on the quality of prepared mixes.

The basic function of a burner is the mixing of fuel with air in a demanded parity for a full combustion of fuel. Air lack leads to losses of heat because of an incomplete combustion and to environmental contamination by the products of an incomplete combustion. With the increase in surplus of air, losses of fuel grow with leaving gases.

At an incomplete combustion of fuel properties of ready aspahlt-concrete mixes also worsen. The fuel rests can reduce viscosity of bitumen, and fuel can be besieged on large particles of the filler which predetermines formation on these particles of a layer and the subsequent insufficient wetting of these particles by bitumen. It reduces durability of the ready asphalt-concrete, made by a asphalt-mixing installation.

The burners are classified by following criteria: factor of surplus of air; percent of leak of air; relative losses in the case; temperature of air submitted from ventilator; percent of the moisture removed from the filler; temperature of the prepared mix; fuel use; degree of a filler heating .

The majority of modern burners represent the compact design intended for work on a liquid, gaseous and firm fuel. And by the way, the transition from one kind of fuel to another can be made by means of insignificant adjustments.

Gaseous fuel includes both natural gas, and steams of oil fuel. For the liquid fuels there are bitumen, black oil and other processings of liquefied of oil fuel. Firm fuel is a coal dust and various hydrocarbons.

For equipment of asphalt-mixing installations of the firm Benninghoven (Germany) are used burners Rax-Jet Turbo of diesel fuel, gaseous fuel (natural gas, biogas, etc.), liquid gas (propane, butane, etc.), firm fuel (coal, biomass, peat, etc.). At use of diesel fuel under a high pressure (in a combination with compressed air) it is put through an atomizer spray in a head part of a burner where it mixes up with a stream of air going from the fan, and it is set on fire by an igniter device working on propane. The stable pure flame provides an effective heating of the inert material which is in area of drying.

By means of the synchronised knot of management at all ranges an optimum hashing of fuel with air is reach which provides an effective combustion of a fuel mix.

Heating devices provide preliminary heating of viscous kinds of fuel (fats, black oil and oil waste). It provides an ideal viscosity of fuel that allows an effective combustion excluding negative influence on environment.

At operation of gas burners, gas through gas-distributingthe device equipped with safety and control devices, moves to the head part of a burnerand under the pressure of 300 mbar – through a gas-distributing ring where it mixes up with air submitted by the fan. The [rofitability and a non-polluting combustion of fuel is thus provided.

At use of liquid gas burners propane, butane and other mixes are stored in special capacities, whence by means of a high pressure pump move under the pressure of 10 bar to a burner on which there is mounted a gas-distributing device.

By means of the dosing out gate fuel in the set volume is injected through a special atomizer into the head part of a burner where it is set on fire and burns out.

At operation of burners of firm fuel coal, biomass, peat, etc. are initially lead up to powder-like conditions, and are delivered on to ABZ and they are stored in a special silo protected from pressure differences. At the exit from a silo there's mount a system of dispensing which provides giving out the powder-like fuel with measured doses to the pneumatic pipeline in a burner.

The distributive chamber established in a burner that provides universal, even distribution of fuel. In the head part of a burner an optimum hashing of fuel and air with a subsequent pure combustion of the given fuel mix is reached. The use of a bad quality fuel dust under the condition of application of a strengthened secondary supporting flame is supposed.

The modeling line of burners Rax-Jet Turbo can be delivered as a universal burners with possibility of use of all the listed above fuel kinds. The developed system of adjustment allows an operator ABZ to choose a necessary kind of fuel. For transition from one kind of fuel to another doesn't require a mechanical change in the design of burners. Now besides the well-known burners Rax-Jet Turbo the firm Bennighoven lets out models of a burner of new series Evo-Jet. The basic difference from parallelly produced model is that air for forcing gets into the burning chamber not from below, but comes horizontally from the side of an end face of a drying drum from above and from below, it assumes an economy of fuel for creation of an effective gas mixture. The particular feature of a design of burners Evo-Jet – in a choice in optimum distance of air-collecting channels from the end face of the drum, allowing to catch warm air and push it into the combustion chamber at temperature of 20-40 0Ñ above the ambient temperature for achievement of effective creation of a fuel mix. According to the firm Bennighoven, at a capture of warm air for blowing the economy of fuel is by 1 t of the ready mix from the burners Evo-Jet makes 1 % in comparison with burners of series Rax-Jet Turbo.

Company Lintec (Germany) at the delivery of asphalt-mixing installations assembles them with both burners of own manufacture, and the combined burners of the leading European manufacturers.

Recently in delivered asphalt-mixing installations to regions of Russia the company Lintec uses burners of the company SAACKE GmbH and Co KG. First of all it concerns burners of type TeminoxR, GS, LS, GLS with capacity 5,4-18,5 ÌÂÒ, working on natural gas, diesel fuel.

It is necessary to notice that for purer combustion of black oil in special burners the company Lintec uses filters for clearing black oil from big impurity, than sizes applied in Europe.

The burneres are subdivided into monoblock and two-block (without a fan). The equipment varies depending on a concrete situation (operation on natural gas, diesel fuel, a combined execution). Electronic adjustment of a parity "fuel-air" is provided for all types of burners. Mechanical – only for monoblock burners.

The burner TeminoxR, GS, LS, GLS consists of an ardent pipe with a device for mixing air and fuel and body in which are placed the fan (at monoblock execution), air valves and a box of electric connections. Behind the retaining washer which is in a conic part of the ardent pipe, there is a mixing submitted under the pressure of fuel and air. There are two standard lengths of the ardent pipe for a various thickness of setting. A special execution of the mixing device, distribution and a way of adding-in gas into a burner are the guarantors of an extremely low emissions of oxydes nitrogen.

Through the centre of the mixing device pass: a liquid-fuel tube (in the combined torches), a tube of primary gas, an igniter and a pipe of primary air. Concentrically the given group of devices is covered by the retaining washer which can be moved on an axis in a conic bell. It allows to support an optimum level speed of the air expiration, irrespective of a burner's productivity. Concentrically round the retaining washer the gas tubes which number depends on the size of a burner are located. The exit of natural gas is carried out in the head part of the ardent pipe. Separate groups of elements in a burner are located visibly and are easily accessible. Demount of the liquid-fuel tube, gas tubes, retaining washer during maintenance service comes easy.

At the heart of reception of extremely low emissions of oxides nitrogen at gas burning the use of three interconnected mechanisms of descending NOx lies. Thanks to the division of natural gas into the primary and secondary the burning of fuel is carried out step by step. The primary burning provides low emissions of the oxides nitrogen, on one hand, at the expense of high degree of the preliminary mixing of primary gas and primary air, on the other hand – because of the raised factor of surplus of air in the zone of primary combustion.

Smoke gases of the first stage of burning reduce the partial pressure of oxygen in the fuel mix at the second stage of burning (secondary combustion) – the process similar to circulation of smoke gases. The secondary burning is stretched to all the length of the top internal chamber, providing an additional high thermal emission along all the way of the reaction course, allowing to lower temperature peaks in the flame.

Manufacture of monoblock burners is one of the basic directions of activity of the firm Ammann (Germany). Thus the great attention is given to compatibility of the drying agreggate and the burner.

For modular monoblock the burners of firm Ammann the complete design, low noise level, economical consumption of energy, optimum burning and low level of emissions in atmosphere are characteristic.

The burners of the firm Ammann work using any kind of fuel – black oil, coal and natural gas, and also the combined fuel – are adjusted everyone in process head-mount according to the specific external conventions.

The basic capacities, a bunker of hot materials and a bunker of a ready mix, are isolated which promotes the prevention of energy loss.

With ideas for reduction of the expense of fuel by the firm Teltomat (Germany) on asphalt-mixing installations is provided a use of high-efficiency modern burners from the leading European manufacturers. The application of various kinds of fuel – gaseous (natural gas), liquid (diesel fuel, black oil, etc.), firm (coal dust) is possible.

The great attention is given to optimisation of the sizes and configuration of fire chambers of the drying drums and oil coppers under certain kinds of fuel.

 A close attention is given also by the Italian manufacturers of asphalt-mixing installations to the questions of the economy and full combustion of fuel.

So, the firm Bernardi assembles produced asphalt-mixing installations with the universal burners working on usage of diesel fuel, black oil or natural gas.

The burner's design is executed with a special heating chamber adapted for regulation of a flame's length. In an internal part of the burner along with the disk located there, having an aperture for passage of a flame, a special latch equipped with a screw controller, increasing or reducing flame, setting an optimum temperature for burning is provided.

Maintenance of an air parity and fuel for burning is reached electronically through an inverter mounted to the motor of the fan at service.

For reduction of the fuel expense for the drying drums and boilers of the firm Marini there are established burners of the leading world manufacturers – ABS, Argomat, Riello and others.

The delivered burners for asphalt-mixing installations are capable to work on diesel fuel, black oil, gas. The delivery of combined burners working on two or more kinds of fuel is possible.

For lowering in the fuel expense in asphalt-mixing installations by the firm Marini are mounted the drying drums of the big overall dimensions (in length and diameter) that provides more time to process the drying and heating of stone materials. The bigger attention is paid to a choice of an optimum form of shovels in the design of drying drums for the increase of efficiency in drying and heating of materials.

On asphalt-mixers of ÐÒ-50 company IPK "Rotor" (Russia) are applied burners of the firm Weishaupt (Germany) working on natural gas, liquid fuel (oven, diesel or top internal black oil), or combined, i.e. working both on one, and on another kind of fuel. Thus full combustion is provided with a good heating of fuel in a tank and in a high-speed heater, application of a powerful smoke-sucker, electronic devices of control and an automatic maintenance of temperature modes and depression in top internal space.

The great attention is paid to the decrease in the expense and completeness of combustion of fuel by the firm Astec (USA) in asphalt-mixing installations of a continuous action.

A certain interest represents in design of a drying-mixing drum of a technology double drum (Double barrel) used in asphalt-mixing installations of the firm Astec .

The advantage of the design Double barrel is in a possibility of a better drying of stone materials at the expense of their moving in full length of the drum and a smaller change of properties in bitumen at the expense of its injection in the external drum isolated from the direct influence of a burner and top internal gases.

Firm Astec equips the asphalt-mixing installations by multifuel burners STAR-JET. Burners Star-Jet can work at all grades of liquid fuel, natural and liquefied gas. In case of use of two kinds of fuel it is necessary to define a primary fuel and to establish a separate line for preparation and distribution of a reserve fuel.

The optimum feature of burners Star-Jet is the convenience of installation of a burner with a blast engine on drying installations in the conditions of the limited areas.

The flame form is established by moving of the regulating lever from outside burners which is connected directly with adjustable blades of a swirler. This feature considerably reduces the adjustment time at initial start-up or change of disposition of the installation, providing an exact adjustment when it is required to change a form and intensity of flame.

A certain interest is represented also by new burners Astec Phoenix of series Phoenix Talon, Phoenix Phantom, Phoenix Coal and Wispersed.

The burners Phoenix Talon are characterized by a high overall performance and a low level of emissions. In the burner's design the system of sound suppressing, providing comfortable conditions for operators is provided at burner's work.

The burners Phoenix Talon provide a smaller current consumption, a compact form of flame and thanks to the drives of variable frequency on fuel and air giving provide an exact dispensing and economy of fuel.

The burners Phoenix Phantom are used for burning of gas fuel in top internal units in the conditions of increased requirements for restriction of harmful emissions.

Working in a mode of an impoverished mix there there is an effective hashing of air and fuel before burning, providing a compact size of flame which allows an increase of an overall performance of the burner at full combustion of fuel.

The burners Phoenix Coal are intended for use of coal fuel. Thus oil or gas can be used as an auxiliary fuel.

According to the American scientists, the burning of coal makes the atmosphere less soiled. In the near future the use of coal as fuel ABZ is planned in the USA. Now at 90 % of them it is authorised to burn coal as fuel.

The burners Wisper-Jet are reliable and easy-to-work, can be used at fuel or gas burning. Thanks to a contact flame they are suitable for work with the drying drums of practically any design without a necessity of adjustment.

A compact form of flame of Wisper-Jet practically excludes an overheat of the drum and does not demand a difficult form of fire updating for a better efficiency of combustion.

The Turkish firm E-poppy assembles their asphalt-mixing installations with burners of the firm Baltur (Italy) or Cuenod (France), of capacity from 8,7 to 23,3 MVt, depending on productivity of installation. These burners can be gas, diesel, black oil or combined using at will of a customer.

One of complete set variants of asphalt-mixers OAO"Kredmash" (Ukraine) is their equipment with block burners of Belorussia production, well proved themselves during their operation.

The burners are equipped with a duty fan, igniter , shut-off and safety valves, pressure gauges of fuel and air, depression in drying drum, control gauges of flame of igniter and a basic burner.

The block of management provides a trouble-free work of burning devices in an automatic mode. Regulation of thermal capacity allows to provide an economy of fuel at the minimum loadings. An available possibility of selection in an optimum parity fuel-air promotes a low specific expense of fuel (up to 6,5 kg/t of liquid fuel or up to 8 m3/t of gaseous fuel) at conformity of products' emissions of combustion according to the ecological norms.

A full combustion of fuel is provided with a good heating, application of a powerful smoke-sucker, automation of burining process.

The work analysis of asphalt-mixing installations of foreign manufacture demonstrates that manufacturers of asphalt-mixing equipment give a great attention to the economy and completeness of fuel combustion at preparation asphalt-concrete mixes at the factories.

At the objects of road-building in Russia there are maintained mainly asphalt-mixing installations of OAO "Kredmash" (Ukraine). Their quantity in the park structure of asphalt-mixing equipment exceeds over 70 %. And more than half of them have service life more than 15-20 years.

Inspection before the release of asphalt-mixing installations of OAO "Kredmash" and Teltomat, made by MADI(GTU) in 2003-2005, showed that burners used in their designs do not meet the modern requirements shown to the fuel systems of asphalt-mixing installations.

The available single occasions of post-equipping of the asphalt-mixing installations at their modernisation by the modern burners of firms Benninghoven (Germany), Oerti Indu Flame (Switzerland), etc. showed positive results at the economy and completeness of fuel combustion at preparation of asphalt-mixing mixes.

The interdepartmental program of the development of the road mechanical engineering of Russia in 2001-2005 provided working out and introduction of dimensins of some modern burners of the domestic production. However manufacturing and their introduction for some reasons of organizational and technical character didnot occurred.

In connection with an imperative need for modernisation of the existing ABZ and a prospective increase in the release of asphalt-mixing installations in Russia by the domestic producers it is especially important to equip with the fuel systems of modern burners working on all kinds of fuel, at its economy and completeness of combustion with a view of maintenance of constantly increasing requirements to quality of the prepared mixes on ABZ.