GB2100848A - Tarmacadam producing apparatus - Google Patents

Abstract

A tarmacadam producing plant including a pair of bitumen storage tanks 10 and an aggregate drier 11. The drier comprises a rotary drum 12, open at either end and has means for passing stone between its ends. Storage tanks 10 are provided with heat exchangers which are coupled to a boiler 21. Hot gases from the associated combustion 22 are fed into the drum 12 via a fixed sleeve 27, which surrounds a perforate portion of the drum 12. Also coupled to this sleeve are further combustion means 26. A heat exchanger 34 is provided at the outlet end of the drum to recapture waste heat. <IMAGE>

Description

SPECIFICATION Tarmacadam producing apparatus This invention relates to apparatus for producing tarmacadam.

Tarmacadam production apparatus consumes energy in the form of heat in two important areas: the maintenance of bitumen at a temperature at which it is fluent, and the drying of the aggregate before it is mixed with bitumen. In existing apparatus the bitumen is generally heated by an electrical coil and the aggregate is dried by oil or gas burners acting directly on it. The operation of this plant is expensive and wasteful.

It is an object of the present invention to provide apparatus for the production of tarmacadam, which is more economic to run and more energy efficient.

From one aspect the present invention consists in apparatus for producing tarmacadam including a storage tank for bitumen having a heat exchanger disposed to heat bitumen in the tank, means for circulating fluid through the heat exchanger, combustion means for heating the fluid before it passes through the heat exchanger, an aggregate drier and flue means for feeding combustion gases generated by the combustion means into the aggregate drier to dry, at least partially, the aggregate therein.

Preferably the aggregate drier includes a rotary drum, in which case the flue means may include a rotary coupling with the drum. For example, the coupling may be constituted by a sleeve, which surrounds a portion of the drum or forms an inlet to the drum. The portion of the drum may be slotted, perforate or otherwise open to allow gas to enter the drum. The apparatus may include means, such as a fan, for driving or drawing the combustion gas into the drum. Alternatively the gas may be introduced by a generally axially extending flue.

The apparatus may include further combustion means for supplying hot gas to the aggregate drier. In the case where the drier includes a rotary drum, the further combustion means may be coupled to the drum by a rotary coupling, which may be the aforementioned sleeve.

The apparatus may further include a heat exchanger disposed to collect heat from gases leaving the aggregate drier, the heat exchanger being connected to one or both of the combustion means to pre-heat the combustion air and/or to heat the liquid in the circulating means.

The or each combustion means may be coal fired and may include an automatic stoker. The combustion chamber of the or each combustion means may be water-jacketed and the jacket may be connected to the means for circulating fluid.

The first mentioned combustion means may include a boiler.

From a second aspect the invention comprises a material drier comprising a chamber, means for passing material through the chamber, combustion means, external to the chamber, for heating gas and means for driving or drawing the heated gas through the chamber to dry the material.

The chamber may be constituted by a rotary drum, which may have a material inlet at one end and a material outlet at the other. The combustion means may be coupled to the drum by a rotary coupling, for example by a sleeve, which surrounds a portion of the drum or forms an inlet to the drum. The portion of the drum may be slotted, perforate or otherwise open to allow gas to enter the drum. The drier may further comprise a heat exchanger mounted at the outlet of the chamber to take heat from the gas leaving the chamber. This heat may be utilised to pre-heat the combustion air supplied to the combustion means.

The combustion means may be coal-fired and may include an automatic stoker.

From a third aspect the invention may include a storage tank including a heat exchanger disposed therein for heating material in the tank.

The heat exchanger may be coupled to means for circulating liquid therethrough and combustion means may be provided for heating the liquid before it passes through the heat exchanger. The heat exchanger may extend vertically in the tank.

The tank may be provided with a hollow jacket, in which case the combustion gas may be passed through the jacket.

The heat exchanger may be provided with a thermostatic control valve. Means may be provided for adjusting the temperature set on the control valve in accordance with at least one of the following: the rate of flow of material into or out of the tank, the level of material in the tank and the operating cycle of any plant associated with the tank.

Preferably the storage tank is for storing bitumen, in which case it may form part of a tarmacadam production apparatus.

The invention may be performed in a number of ways, a specific embodiment of which will now be described, by way of example, with reference to the accompanying drawing which shows the storage tanks of a tarmacadam producing plant in vertical section and associated heating apparatus and an aggregate drier schematically in plan view.

Tarmacadam is generally produced by spraying fluent bitumen on to an aggregate in a mixing mill.

Frequently fillers such as Portland cement are also added. Bitumen is solid at normal ambient temperatures and it is therefore necessary to maintain it at a temperature above its melting point, typically at 130-1 600C during the manufacture of the tarmacadam. As the bitumen is frequently stored in 8,000 gallon tanks considerable heat is needed to achieve and maintain this temperature. At present this heat is supplied by an electric coil, which is extremely expensive to operate.

For successful mixing the aggregate must be dry and it is preferably at a temperature similar to that of the bitumen. In existing apparatus the aggregate is dried and heated by direct contact with the flames of oil burners. This is again a very expensive form of heating, and as the burners are of necessity contained inside the drying apparatus, they are difficult to repair and maintain.

A part of a tarmacadam producing plant in accordance with the invention is shown in the drawing. This part includes a pair of bitumen storage tanks 10 and an aggregate drier, generally indicated at 11. The drier comprises a rotary drum 12, open at either end, and has a spiral flange (not shown) extending along its inner surface. A conveyor (not shown) spills the aggregate into the drum 12 at an inlet 13. As the drum 12 rotates, it continuously turns the aggregate, whilst feeding it to an outlet 14, where it is deposited onto a further conveyor (not shown), which transports the aggregate to the mill (not shown). Heated gas is fed into the drum 12, in a manner described below, and this gas is drawn along the length of the drum by a fan 15, which is disposed adjacent the outlet 1 4.

The storage tanks 10 are provided with vertically extending heat exchangers 16, which are connected, in parallel, to a hot water or steam supply line 1 7 by respective valves 1 8 and to a return line 1 9 by respective valves 20. The supply line 1 7 and the return line 1 9 are connected to a boiler 21, which is fired by an automatically stoked coal-fired burner 22. A pump 23 is connected in the return line 1 9 to circulate the water through the boiler 21 and hence through the heat exchangers 1 6 to heat the bitumen in the tanks. The burner 22 is preferably of the type which has a water-jacketed combustion chamber, in which case the water jacket is connected into the water supply circuit by lines 24 and 25.

A similar burner 26 is provided to supply heated gas to the drier 11. The output of the burner 26 is connected to a fixed sleeve 27, which surrounds the rotary drum 12. Sliding seals are provided between the sleeve 27 and the drum 12, and the portion of the drum, which is surrounded by the sleeve, is slotted, at 28, to allow the heated gas to be drawn into the drum by the fan 1 5. The slots 28 are normally covered by a wire grid to prevent aggregate falling through them. It will be appreciated that any suitable opening or configuration of openings may be used.

The boiler 21 is connected to the sleeve 27 by a flue 29, such that the hot exhaust gases which have passed through the boiler are also passed through the drier 11. A fan 30 can be provided in the flue 29 to assist the flow of the exhaust gas into the drier. When the drier is not in use the exhaust gases can be vented to atmosphere through a suitable chimney, or, if the storage tanks are provided with a suitable hollow jacket, passed through these jackets to help maintain the temperature in the tanks.

The waterjacket of the burner 26 may be connected into the water supply circuit by lines 31 and 32.

It will be appreciated that the arrangement described above uses cheap readily available solid fuel and that it is thermally very efficient. Further the heat sources for the drier 11 are external to the drum 1 2 and hence are readily and easily maintained.

The thermal efficiency of the system can be further increased by disposing a heat exchanger between the outlet 14 and the fan 1 5. If a gas/air heat exchanger is used, the heated air can be fed to burners 22 and 26 to provide pre-heated combustion air. Alternatively a gas/water heat exchanger could be used, in which case the operator or a control svstPm could have the choice of pre-heating the combustion air of the burners by further heat exchangers or feeding the heated water into the hot water circuit.

Instead of surrounding a portion of the drum 11, the sleeve 27 may form the inlet to the drum or alternatively the heated gases may be introduced into the drum by an axially extending flue.

The valves 18 and/or the burners 22 and 26 may be thermostatically controlled. A control system may be used to optimise the operation of the apparatus for example by controlling the opening and closing of the valves, the rate of stoking of the burners, the operation of the pump and the rotational speed of the fans. In addition the control system may take into account the level of bitumen in the tanks, the rate of flow from the tanks and the period for which the bitumen will remain in the tanks. The system may arrange for the tanks to be kept at different temperatures in accordance with their planned order of use.

More than two bitumen tanks may be connected to line 1 7 and 19, via the connections at 33. All the lines, the tanks and the drier are preferably fully lagged to reduce heat loss. The stone leaving the drier may be at a temperature of about 1200-1400C.

Claims (20)

1. Apparatus for producing tarmacadam including a storage tank for bitumen having a heat exchanger disposed to heat bitumen in the tank, means for circulating fluid through the heat exchanger, combustion means for heating the fluid before it passes through the heat exchanger, an aggregate drier and flue means for feeding combustion gases generated by the combustion means into the aggregate drier to dry, at least partially, the aggregate therein.

2. Apparatus as claimed in claim 1, wherein the drier includes a rotary drum and wherein the flue means includes a rotary coupling with the drum.

3. Apparatus as claimed in claim 2, wherein the coupling is constituted by a sleeve, which surrounds a portion of the drum or forms an inlet to the drum.

4. Apparatus as claimed in claim 3, wherein the portion of the drum is slotted, perforate or otherwise to allow gas to enter the drum.

5. Apparatus as claimed in claim 1, wherein the drier includes a rotary drum and the flue means extend generally axially into the drum.

6. Apparatus as claimed in any one of claims 2 to 5, further including means for driving or drawing the combustion gas into the drum.

7. Apparatus as claimed in any one of the preceding claims, including further combustion for supplying hot gas to the aggregate drier.

8. Apparatus as claimed in claim 7, wherein the gases from the further combustion means are introduced into the drier by the flue means or a part thereof.

9. Apparatus as claimed in any one of the preceding claims, further including a heat exchanger disposed to collect heat from gases leaving the aggregate drier, the heat exchanger being connected to one or both of the combustion means to preheat the combustion air and/or to heat the liquid in the circulating means.

10. Apparatus as claimed in any one of the preceding claims, wherein the or each combustion means is coal-fired.

11. Apparatus as claimed in claim 10, wherein the combustion chamber of the or each combustion means is water-jacketed and the jacket is connected to the means for circulating fluid.

12. A material drier comprising a chamber, means for passing material through the chamber, combustion means, external to the chamber, for heating gas and means for driving or drawing the heated gas through the chamber to dry the material.

13. A drier as claimed in claim 12, wherein the chamber is constituted by a rotary drum open at each end.

14. A drier as claimed in claim 13, wherein the combustion means is coupled to the drum by a rotary coupling which surrounds a portion of the drum or forms an inlet to the drum.

1 5. Apparatus as claimed in claim 14, wherein the portion of the drum is slotted, perforate or otherwise open to allow gas to enter the drum.

1 6. A storage tank including a heat exchanger disposed therein for heating material in the tank.

17. A storage tank as claimed in claim 16, having a vertically extending heat exchanger and a hollow jacket, means for coupling the heat exchanger to combustion means for heating liquid before it passes through the heat exchanger and means for connecting the hollow jacket to the combustion means so that combustion gases therefrom are circulated through the jacket.

1 8. Apparatus for producing tarmacadam substantially as hereinbefore described with reference to the accompanying drawing.

1 9. A material drier as hereinbefore described with reference to the accompanying drawing.

20. A storage tank substantially as hereinbefore described with reference to the accompanying drawings.