In relating to the use of Liquefled Air for Effecting Economies in connection with Power Generating. Works, where the Demand for Power is Subject to Large Fluctuations.
Year: 1898

page_text: Date of Application, 23rd Dec., 1898
Complete Specification Left, 20th Sept., 1899-Accepted, 16th Dec., 1899
Invention relating to the use of Liquefled Air for Effecting Economies
in connection with Power Generating. Works, where the Demand
for Power is Subject to Large Fluctuations.
I, EDGAR CHARLES THRUPP, Civil Engineer, of Southdene, Ashley Park Road,
Walton-on-Thames, Surrey, do hereby declare the nature of this invention
to be as follows:-
It is a well recognised fact that one of the chief obstacles in the way of attain-
ing the highest efficiency and economy in many works where power is used, lies
in the fluctuating nature of the demand. In many electric light stations, for
instance, the average output throughout the year is often less than one tenth
of the maximum output.
My invention is intended to apply particularly to electric power stations
where steam, gas or oil engines are the prime movers, but it may also be applied
to other works. For the sake of clearness the following description of the
invention relates to its application to an electric power station.
In accordance with my invention the heat engines or prime movers may be
worked continuously day and night, if required, and always at a sufficiently
high and sufficiently uniform load to give the most economical results. During
the periods when the demand for electric current is small, part of the power
developed is applied in the usual manner to drive the dynamos supplying current
to the mains. The remainder of the power is applied to drive compressers in
connection with apparatus for liquefying air.
The compressed air is cooled nearly down to the temperature of the atmos-
phere by being passed through coils in the open air, or having a circulation of
water. It then passes to a second series of coils immersed in a tank of water
or brine, or other suitable substance, surrounding another tank of water or
brine containing a third series of coils and surrounding the reservoir to store the
liquid air, with a small intervening space filled with slag wool or other non-
conducting material.
The compressed air traverses the coils in each tank, preferably from the top
to the bottom and passes away to the expanding and liquefying apparatus, and
the liquid is delivered into the storage tank. A convenient arrangement is to
make the liquid air tank circular in plan and the concentric brine tanks hexa-
gonal, with wrought iron or steel plate sides to bend slightly with the expansion
of the ice in the tanks. The space between the circular reservoir and the inner
hexagonal tank is then filled with slag wool. Three or more brine tanks may
be used if desired.,
In addition to the compressed air cooling pipes, two other sets of pipes or
coils are immersed in each concentric tank. One, of these is used to convey the
waste cold air from the liquefier back to the compressor, and serves to cool the
brine and therefore the compressed air. Any air evaporated in the storage
tank cylinder may be either discharged into the waste cold air coils or delivered
by pipes to the lower part of the slag wool jackets through which it can per-
colate and escape to the atmosphere.

page_text: The third set of pipes in the brine tanks is used to evaporate the liquid air
when it is required for use as follows. When the demand for electric current
rises above a certain rate of output, the liquid air is pumped as required into
the third set of pipes in the brine tanks and is partially or wholly evaporated
by heat derived from the brine, and thus lowers the temperature of the brine
and renders it capable of cooling fresh supplies of compressed air. The liquid
or evaporated air is further warmed and expanded under pressure by the appli-
cation of heat. The heat required for this purpose may be derived from the
atmosphere or from the earth, but if the coils are exposed to the atmosphere
they are liable to become coated with snow or ice which interferes with the
warming efficiency of the coils, and if placed in the earth the freezing of the
earth produces a like result. I therefore prefer to use the heat from one or more
of the following sources which can easily be regulated.
In the case of steam engine stations:-
1). The exhaust steam from the engines applied either directly to the outside
of the air coils or from the condenser water.
2). The waste flue gases from the boilers.
3). The water which has passed through the condenser during the period
when the liquid air is not required to be evaporated, and is stored in a reservoir
to be cooled for further use.
In the case of gas or oil engine stations:-
1). The circulating water from the engine cylinder jackets.
2). The waste gases from the engines.
3). The gas coolers, if the gas to drive the engines is generated on the pre-
mises in gas producers."
The hot compressed air thus produced is applied to work engines similar to
steam engines and used for driving dynamos or other machinery.
I prefer to use compound engines, and to re-heat the air exhausted from the
higher pressure cylinders, by passing it through coils or pipes heated by one
of the hottest of the beforementioned sources of waste heat, before delivering it
to the lower pressure cylinders.
In some cases it is desirable to burn fuel to evaporate or super-heat the air,
as for instance, where a large proportion of the liquid air prepared during
24 hours, is required to be used in less than 3 hours, or where cheap fuel is
available.
Dated this 23rd day of December 1898.
Invention relating to the use of Liquefied Air for Effecting Economies
in connection with Power Generating Works, where the Demand
for Power is Subject to Large Fluctuations.
I, EDGAR CHARLES THRUPP, Civil Engineer, of Southdene, Ashley Park Road,
Walton-on-Thames, Surrey, do hereby declare the nature of this invention
and in what manner the same is to be performed, to be particularly described
and ascertained in and by the following statement:―
It is a well recognised fact that one of the chief obstacles in the way of attain-
ing the highest efficiency and economy in many works where power is used, lies
in the fluctuating nature of the demand. In many electric lighting stations for
instance, the average output throughout the year is often less than one tenth
of the maximum output.
My invention is intended to apply particularly to electric power stations

page_text: where steam, gas or oil engines are the prime movers, but it may also be applied
to other works. For the sake of clearness the following description of the
invention relates to its application to an electric power station.
In accordance with my invention the heat engines or prime movers may be
worked continuously day and night, if required, and always at a sufficiently
high and sufficiently uniform load to give the most economical results. During
the periods when the demand for electric current is small, part of the power
developed is applied in the usual manner to drive the dynamos supplying current
to the mains. The remainder of the power is applied to drive air compressors in
connection with apparatus for liquefying air. The compressed air is cooled
nearly down to the temperature of the atmosphere by being passed through coils
in the open air, or having a circulation of water. It then passes to a second
series of coils immersed in a tank of water or brine, or other suitable substance,
surrounding another tank of water or brine containing a third series of coils
and surrounding the reservoir to store the liquid air, with a small intervening
space filled with slag wool or other non-conducting material.
The compressed air traverses the coils in each tank, preferably from the top
to the bottom and passes away to the expanding and liquefying apparatus, and
the liquid is delivered into the storage tank. A convenient arrangement is to
make the liquid air tank circular in plan and the concentric brine tanks hexa-
gonal, with wrought iron or steel plate sides to bend slightly with the expansion
of the ice in the tanks. The space between the circular reservoir and the inner
hexagonal tank is then filled with slag wool. Three or more brine tanks may
be used if desired.
In addition to the compressed air cooling pipes, two other sets of pipes or
coils are immersed in each concentric tank. One of these is used to convey the
waste cold air from the liquefier back to the compressor and serves to cool the
brine and therefore the,compressed air. Any air evaporated in the storage
tank cylinder may be either discharged into the waste cold air coils or delivered
by pipes to the lower part of the slag wool jackets through which it can per-
colate and escape to the atmosphere.
The third set of pipes in the tanks is used to evaporate the liquid air
when it is required for use as follows. When the demand for electric current
rises above a certain rate of output the liquid air is pumped as required into
the third set of pipes in the brine tanks and is partially or wholly evaporated
by heat derived from the brine, and thus lowers the temperature of the brine
and renders capable of cooling fresh supplies of compressed air. The liquid
or evaporated air on leaving the brine tank coils is further warmed and ex-
panded under pressure by the application of heat. The heat required for this
purpose may be derived from the atmosphere or from the earth, but if the coils
are exposed to the atmosphere they are liable to become coated with snow or
ice which interferes with the warming efficiency of the coils, and if placed in
the earth the freezing of the earth produces a like result.
I therefore prefer to use the heat from one or more of the following sources
which can be easily regulated.
In the case of gas or oil engine stations:-
1). The exhaust steam from the engines applied either directly to the outside
of the air coils or from the condenser water.
2). The waste flue gases from the boilers.
3). The water which has passed through the condenser during the period
when the liquid air is not required to be evaporated and is stored in a reservoir
to be cooled for further use.
In the case of gas or oil steam engine stations:-
1). The circulating water from the engine cylinder jackets.
2). The waste gases from the engines.
3). The gas coolers, if the gas to drive the engines is generated on the pre-
mises in "
gas producers."

page_text: The hot compressed air thus produced is applied to work engines similar to
steam engines and used for driving dynamos or other machinery.
I prefer to use compound engines, and to re-heat the air exhausted from the
higher pressure cylinders, by passing it through coils or pipes heated by one
of the hottest of the before-mentioned sources of waste heat, before delivering it
to the lower pressure cylinders.
In some cases it is desirable to burn fuel to evaporate or super-heat the air,
as for instance where a large proportion of the liquid air prepared during
24 hours, is required to be used in less than 3 hours, or where cheap fuel is
available.
The accompanying drawing shows a plan of the apparatus (diagrammatically)
as it may be applied to an electric power station driven by steam. A repre-
sents one of the steam engines driving a dynamo. B is a triple expansion
steam engine driving a three stage air compressor in which b₁ b₂ b₁ are the
three steam cylinders and c₁ c c are the three air compressing cylinders and
D is the fly wheel. E is a water tank containing two sets of coils of cooling
pipes through which the compressed air passes in travelling from the cylinders C₁
& C₂ C3 respectively. On leaving the cylinder C, the compressed air travels
through the pipe f to the first set of cooling coils which may be in the open
air or in a tank of water having a supply of cooling water circulating through
it. The compressed air then passes to a second series of coils G G immersed in
the outer tank of brine H H which surrounds another tank of brine J J con-
taining the third series of compressed air cooling coils L L. The coils in the
brine tanks are represented in the drawing (by single lines) as passing only
once round each tank, but this is done simply for the sake of clearly indicating
the circuits traversed by the air. The actual arrangements of the coils consists
of one or more sets of coils hexagonal in plan but placed one above the other
forming a kind of spiral circuit. The outer tank is enclosed by a non-conducting
wall MM, shaded in full lines on the drawing. The division between the
tank H H and the tank J J'is indicated by the line h h and the inner wall of
the tank J J is indicated by the line j j. K is the storage tank for the liquid
air, and the space between K and j; which is shaded in dotted lines on the
drawing, is filled up with slag wool or other non-conducting material. The
compressed air in passing through the coils G G and L L is cooled down far below
the temperature of the atmosphere and is liable to deposit snow which may be
separated by means of boxes such as N N in which the velocity of the air is
checked and the snow deposited. These boxes are arranged in duplicate and
provided with valves for shutting off either one to remove the snow, and they may
be connected at any convenient point on the coils where the temperature is
low enough to form snow.
On leaving the coils L L the compressed air is delivered to a turbine I
through the valve "n." The turbine is worked by the cold compressed air which
becomes further cooled and partially liquefied in passing through the turbine.
The liquid portion of the air exhausted from the turbine runs into the storage
tank K through the pipe 0 and the gaseous portion passes to the second set
of coils or pipes in the brine tank P P (in the inner tank) and Q Q (in the
outer tank), travelling in the reverse direction and close to the compressed
air. The compressed air cooling coils and the cold exhaust air pipes thus form
a heat interchanger through the medium of the brine in the tanks. The coil Q Q
discharges the air to the pipe R leading back to the compressor.
The turbine assists in driving the compressor through the friction gearing S
and the belt T.
The arrangement of compressor heat interchanger and turbine with their
connections and accesseries is similar to that described in my Complete Specifi-
cation No. 26,767, 1898, the brine tanks and arrangements for evaporating and
using the liquid air being the features of novelty in the present invention.
When it is desired to utilize the store of liquid air, it is drawn from the bottom

page_text: of the tank through the pipe U and forced by the pump V into a third set of
pipes immersed in the brine tanks namely W W in the inner tank and X X in
the outer tank. The heat required to evaporate the liquid air is thus drawn
from the brine and the temperature of the latter is consequently lowered and it
therefore becomes better able to cool the compressed air during the next cycle
of operations. The cooling effect due to the absorption of the latent heat of
evaporation is thus utilized and the process of subsequent liquefaction is facili-
tated. The evaporation takes place under the pressure at which the liquid is
pumped into the coils and the compressed gaseous air produced emerges by the
pipe" and enters one or more of the coils 1, 2 and 3 in succession. These
coils are heated by the various sources of heat already enumerated as available
for the purpose.
For instance, as shown in the drawing coil 1 may be immersed in a tank
containing warm water which has passed through the steam condenser; coil 2
may be heated directly by the exhaust steam from the engines and thus assist in
condensing the steam, and coil 3 may be placed in the flue conveying the waste
gases from the boilers to the chimney.
The compressed air derived from the liquid air is thus delivered to the
engine Y at a high temperature and after passing through the high pressure
cylinder may be reheated in coil 4 (placed in the boiler flue) before entering the
low pressure cylinder of the engine."
The various coils for heating the air may be made in any suitable form
similar to steam boilers, super-heaters or condensers.
The sources of waste heat named will yield enough heat to warm sufficient
air to drive engines of far greater power than the steam plant from which the
waste heat is derived, and it is therefore possible to dispense with a large pro-
portion of the boiler plant which would be required in an ordinary electric light
station for instance, and the condensation of the steam would be rendered easier.
The same arrangement of liquid air storage may be adopted for marine pur-
poses where high speeds are required for short periods, as for instance in the
case of torpedo boats or for channel steamers which are only required to be in
motion for two or three hours a day.
In the event of gas engines being used as the prime movers, the com-
pressor ₁₂ (shown on the drawing) would be driven by a gas engine; the
engine A would be replaced by a gas engine discharging its exhaust gases into
the chamber surrounding the heating coil No. 2, and the water from the cylinder
jackets would be applied to the heating coil No. 1.
If oil engines are used, the waste heat from the exhaust gases and cylinder
jackets would be similarly applied.
When gas, to drive the engines, is produced on the premises, it may be passed
through a pipe or flue containing the heating coils 3 and 4 before entering the
scrubbers or gasholder in order to cool the gas and heat the compressed air.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is:
1) The arrangement of a storage tank for liquid air surrounded by one or
more brine tanks containing heat interchanging coils and liquid air evaporating
coils, in combination with means for liquefying air and means for converting
the liquid air into hot compressed air for use in driving engines substantially
as described.