GB2059898A - Improvements in or relating to airships - Google Patents

Abstract

An airship (1) is provided with means (4) for condensing water vapour from exhaust gases created by burning of fuel for propulsion of the airship, and for collecting the condensate (from 8) for ballast purposes. The water vapour condensing means (4) operate to reduce the temperature of exhaust gases by passing the gases in two-stage heat exchange with coolant. The first stage takes place within a scrubbing tower (5) whereby exhaust gas from a duct (3) is passed in heat exchange with water sprayed on to a bed (6) using a sprayer (10). The second stage of cooling is effected by refrigeration means (30) which uses water as the working fluid, and comprises condenser (37), first evaporator (9) steam/water separator (41), second evaporator (15) and ejector pump (43). <IMAGE>

Description

SPECIFICATION Improvements in or relating to airships BACKGROUND TO THE INVENTION This invention relates to airships.

A problem exists. in operating airships, namely lightening of an airship by consumption of fuel used for propulsion of the airship.

SUMMARY OF THE INVENTION According to the present invention, an airship is provided with means for condensing water vapour from exhaust gases created by burning of fuel used for propulsion of the airship, and for collecting the condensate for ballast purposes.

The water vapour condensing means preferably comprise apparatus whereby the temperature of exhaust gases is reduced by passing the gases in two-stage heat exchange with coolant, the second stage of cooling being effected by refrigeration means.

BRIEF DESCRIPTION OF THE DRAWING An embodiment of the invention will now be described, by way of example only, with reference to the semi-diagrammatic drawing which illustrates part of an airship provided with vapour condensing means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to the drawing, an airship 1 is provided with three diesel engine/ducted fan propulsion units (not shown) for propulsion purposes. Exhaust gases from the diesel engines are collected in a manifold 2 having an outlet duct 3 discharging to condensing means 4 whereby water vapour from the exhaust gases is condensed and the condensate is collected for ballast purposes.

The condensing means 4 comprise a scrubbing tower 5, the lower end of which is connected to the duct 3. The tower 5 houses a bed 6 of packing. (Preferably Raschig rings).

A weir 7 is disposed in the bottom of the tower 5, so as to form a condensate well 8. Also disposed in the tower 5 are a heat exchanger 9 and sprayer manifold 10, (both above bed 6), as well as an evaporator 15, (below the bed 6).

Condensate is removed from the well 8 by a pump 1 6 disposed in a recirculating line 17, passed through a heat exchanger 1 8 also in the line 17, and returned to the tower 5 by way of the manifold 10, which is connected to the line 1 7.

The heat exchanger 1 8 is cooled by a flow of air discharged from a fan 1 9 driven by a motor 20.

The recirculating line 1 7 is provided with a vent valve 25 and a drain valve 26.

A condensate line 27 connects the outlet side of the weir 7 with a ballast tank (not shown), or other suitable collecting chamber.

Cooled exhaust gas is allowed to escape to atmosphere by way of a vent line 28 connected to the upper end of the tower 5.

The internal heat exchanger 9 and evaporator 1 5 form part of refrigeration means 30. Other parts of the means 30 comprise a refrigerant re-circulating line 35, an ejector driving line 36, a heat exchanger 37 cooled by a flow of air provided by a fan 38 driven by a motor 39, a flow restrictor 40, a separator 41 disposed above the evaporator 15, a drain valve 42, an ejector unit 43 and a filling valve 44. The refrigerant is H20.

In operation, hot exhaust gas collected in manifold 2 is cooled in the scrubbing tower 5 in two stages. The first cooling stage takes place in the tower and comprises passage of the gas in counterflow with coolant (cold water) discharged on to the packing bed 6 by the sprayer manifold 10.

The second cooling stage takes place in the refrigeration means 30. Vapour drawn through the heat exchanger 9 is raised in pressure by the ejector unit 43. It is then discharged to the heat exchanger 37 where it is condensed.

The condensate pressure is reduced in passage through the flow restrictor 40 and the condensate partially evaporated by passage through the heat exchanger 9. (The heat exchanger serves as an evaporator in the refrigeration circuit of the means 30, and as a condenser to the exhaust gases in the first-stage coolant circuit).

In the separator 41 steam and water are separated out. The pressure of the separated water rives due to gravity as it drops to the evaporator 1 5 which is disposed well below the separator 41.

In the refrigeration means 30: a) The highest steam pressure (P,) exists in that part of line 36 between the evaporator 1 5 and ejector unit 43.

b) An intermediate steam pressure (P2) exists in that part of line 35 between the ejector unit 43 and the heat exchanger 37, errabling condensation of vapour at about 27"C.

c) The lowest steam pressure (P3) exists in that part of line 35 between the separator 41 and ejector unit 43.

It will be appreciated that the working pressures of the steam flowing in the refrigeration means 30 are quite low, for example, 0.036 bars at 27"C.

In the present example, the ejector unit 43 is driven by vapour generated in the evaporator 1 5, the vapour being tapped off the separator 41. Alternatively, heat energy may be taken from the coolant systems of the diesel engines. In both cases, means are preferably provided whereby the vapour is re-used.

The vapour condensing means 4 is based on the following design parameters.

1. A total of 3 diesel engines in operation each developing 260 SHP at. 1 800 rpm at the airship cruising speed of 75 Knot.

2. Engine exhaust temperature 485"C.

3. Engine exhaust content:- N2 -5510 Ibs/hour 02 -708 Ibs/hour C02-908 Ibs/hour SO25 Ibs/hour H20-431 Ibs/hour 4. Air/fuel ratio 25:1. Total fuel consumption: 287 Ibs/hour.

5. Higher calorific value (H.C.V.) of fuel 19,800 Btu/lb.

6. Composition of fuel 86.3% C, 12.8% H2, 0.9% S.

7. Engine thermal efficiency 35% based on the H.C.V.

8. Airship cruising height 3000 ft. (air pressure 13.2 Ibs/square inch absolute (psia)).

9. Air temperature 21 C at 3000 ft., corresponding to a temperate zone maximum summer temperature.

10. Relative humidity if air taken as 0.8 which corresponds to an absolute humidity of 0.014 lb of water vapour per Ib dry air at 3000 ft.

11. Pumping rate of pump 16-50 gallons/hour.

The-total engine exhaust gas composition includes a total of 43t lb/hr of water vapour, 331 Ib/hr of which is derived from the combustion of the fuel (fuel combustion rate 287 Ib/hr) and the remainder from the humidity of the engine intake air. The dew point of the engine exhaust gas is calculated to be 42to, the corresponding partial pressure of the water vapour in the exhaust gas being 1.20 psia. The exhaust gas must therefore be cooled from 485"C down to 42"C before any condensate appears.To effect a desired condensation rate af 287 Ib/hr, which is equal to the fuel consumption rate, it is calculated that the exhaust gas must be cooled down to 24"C as it is discharged to atmosphere from line 28, at which temperature the vapour partial pressure will be 0.426 psia The first or main cooling stage (recirculating line 17) has a heat load of 523 kW.

It is not usually considered practical to operate air-cooled heat exchangers with a cooling approach of less than 3"C. In the present application, where it is important to keep weight as low as possible, a cooling approach of 6 C is considered more appropriate and thus, 27"C is the temperature of the condensate leaving the air-cooled heat exchanger 1 8 and fed to the top of the packed bed 6 in the scrubbing tower 5 by way of manifold 10. The bed 6 will be about 3ft, X 2ft. X 6ft. deep if a packing such as 2 inch Raschig rings are used, but there are other forms of packing which could allow a smaller bed of lower weight. Condensate enters the heat exchanger 18 at 60"C.

The excellent heat transfer characteristics of a scrubbing tower tend to produce very close approach temperatures at the top of the tower. In the present application it is calculated that the exhaust gas will leave the packed bed 6 at about 29"C having. produced about 85% of the required condensation rate of 287 Ibs/hour. This shortfall is the inevitable consequence of the design air temperature of 21 C and the fact that an overall cooling approach of 3"C is not practical. As stated above, the exhaust gas must be cooled down to 24 C to obtain the required condensation rate.

This problem is overcome by use of the second, i.e. refrigeration, stage. The circuit of means 30 can be very simply made without any moving parts by using an ejector vapour compression system. The condenser cooling load, i.e. the heat to be removed from the exhaust gas to cool it from 29C to 24"C, is only 17 kW. The evaporator (37) heat load is 33 kW.

Preliminary calculations suggest that the refrigerating means 3Q can usefully be exploited in three ways.

I) It can be used to reduce overall weight by suitably apportioning the heat loads taken by the main cooling circuit and the refrigerating circuit. The lattertends to be more effective on an equipment weight basis in removing heat from the exhaust gas at the low temperature end. (The scrubbing tower is more effective at the high temperature end).

2) The use of a refrigerating circuit should enable the airship 1 to operate with an effective ballast system at air temperatures up to 40"C or higher. The airstrip 1 can therefore be operated in tropical conditions.

3) The refrigerating circuit enables fairly clean condensate to be produced from the exhaust gas. By collecting this condensate, it can be used for hot water services such as showers, wash basins etc. on board. Calculations indicate that 1 ton of such water can be collected during an Atlantic crossing. A small, lightweight ion exchanger column may be provided for removal of sulphuric acid or other impurities.

Claims (6)

1. An airship provided with means for condensing water vapour from the exhaust gases created by burning of fuel used for propulsion of the airship and for collecting the condensate for ballast purposes.

2. An airship as claimed in Claim 1, wherein the water vapour condensing means comprise apparatus whereby the temperature of exhaust gases is reduced by passing the gases in twostage heat exchange with coolant, the second stage of cooling being effected by refrigeration means.

3. An airship as claimed in Claim 2, provided with a scrubbing tower containing packing, wherein the first stage of heat exchange takes place in the scrubbing tower and comprises passing the gases in counterflow with coolant discharged on to the packing of the tower.

4. An airship as claimed in Claim 2, wherein the refrigeration means comprise an ejector, a heat exchanger, a flow restrictor and a separator.

5. An airship as claimed in Claim 2, 3 or 4, wherein the refrigerant comprises H2O.

6. An airship substantially as hereinbefore described with reference to the accompanying drawing.