Note: Descriptions are shown in the official language in which they were submitted.
CA 02202111 1997-04-08
This invention relates to a new or improved heating system and
method which are particularly suitable for use at locations where a ready supply of
fuel gas is available. The heating system and process can be operated without
having to rely upon a prime mover or a supply of electricity.
In many situations, and in particular at the production wells of natural
gas fields there is a need to store supplies of water and other fluids such as oil
and diesel fuel. In cold climates it is desirable to locate the tanks for such liquids
underground to protect their contents from freezing. However due to recent
ERCB/AEUB environmental regulations, underground produced water tanks have
10 become prohibitively expensive to install, monitor for leakage, and reclaim or
remove. Above ground tanks are obviously much easier to install, monitor, repair,
and move, but they and their associated piping are subject to freezing during cold
winter weather with the result that at a gas well site, the separator which
separates the gas from liquids may malfunction and carry over liquids into the gas
pipeline, or shutdown on high level. Outdoor wet fuel gas piping can also cause
freezing in regulators and instruments, again causing shutdowns, lost production
and increased operating expenses.
The present invention provides a heating system comprising: a fluid
flow circuit that is connected to circulate a heat transfer fluid between (a) a heat
20 generating location whereat said fluid is heated; and (b) a heat yielding location
whereat heat is extracted from said fluid; said system including a fluid pump for
effecting circulation of the heat transfer fluid, said fluid pump configured to be
energized by the pressure energy of a pressurized gas supply.
Preferably the pressurized gas supply is a fuel gas utilized in a fluid
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lift pump to effect circulation of the heat transfer fluid, and after such utilization fed
to a heater such as a flameless catalytic heater to effect heating of the heat
transfer fluid at the heat generating location. The gas supply need not be at anextremely high pressure, but on the contrary may be at a relatively low pressureprovided that sufficient energy can be obtained from expansion of the gas to drive
the pump that circulates the heat exchange fluid. Depending upon the quantity ofheat transfer fluid to be circulated per unit time, the energy requirement is not
great, since a relatively small pressure head will suffice to drive the circulation,
and indeed the fluid circulation will be assisted by convection forces generated by
changes in fluid density in the heater and in the heat exchanger respectively.
From another aspect the invention provides a method of applying
heat to a liquid in a fluid container to maintain such liquid at a temperature above
a predetermined threshold temperature, said method comprising: providing a fluidflow circuit which includes a heat generating location where heat is supplied tosaid heat transfer fluid, and a heat exchanger within said container whereat heat is
transferred from said heat transfer fluid to the liquid in said container; and
circulating said heat transfer fluid within said fluid flow circuit, said circulating
being powered by the pressure energy of a pressurized gas supply.
To overcome the problems discussed above in relation to producing
natural gas well sites which are subject to freezing problems, the basic solution is
to deliver heat into the problem areas, and to insulate the exterior of the pipes or
tanks to ensure that the inside temperature is maintained above freezing. This
was commonly done hitherto utilizing electrical heating elements and tracing wires.
Where electrical power is not available or not economical, the heating system of
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the present invention can be employed utilizing the pressure and calorific value of
the fuel gas such as natural gas or propane to deliver heat inside insulated piping
or insulated tanks, the heat being transferred to the liquids by suitable heat
exchangers. Typically this will require a fluid flow circuit in which relatively large
volumes of heat transfer fluids such as glycol have to be circulated continuously.
In accordance with the invention it is preferred to effect circulation of
the heat transfer fluid by means of a Gas Induced Fluid Transfer (G.l.F.T.) pump
which is sold by Opsco'92 Industries Ltd., which can utilize fuel gas pressurized at
relatively low pressures to induce the desired flow rates of the glycol heat transfer
10 fluid. For example it is possible to effect a flow rate of 30 U.S. gallons per hour
with a consumption of natural gas of less than about 2.5 standard cubic feet per
hour. All of the drive gas passing through the GIFT pump can be reused in the
heater. To this extent the fluid circulation energy is essentially "free". The gas
induced fluid transfer pump disclosed herein has no moving parts and is
completely maintenance free. Once started it can run continuously without any
operator attention.
The heater may suitably comprise a building heater such as the one
sold under the name Catadyne which is in common use in well site facilities and
which produces infrared radiant energy via a catalytic reaction with no flame. The
20 heat transfer fluid can be circulated through a thinned heat exchanger which is
exposed to the energy of the heater. If this arrangement is installed indoors, then
excess heat from the heater which is not taken up by the heat transfer fluid is not
wasted, but helps to warm the building interior.
The invention will further be described, by way of example only, with
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reference to the accompanying drawings wherein
Figure 1 is a somewhat schematic view of a well site utility tank
heating system incorporating the invention; and
Figures 2a, 2b and 2c are schematic illustrations of fluid pumps
which can be utilized with the system, Figure 2a showing the simplest basic
prototype pump design, while 2b and 2c show some other variations.
The heating system shown in Figure 1 includes a heat exchanger 11
located within a water storage tank 12 and connected in circuit to receive heat
exchange liquid from a heater 13 through a delivery line 14. A first return line part
15 is connected from the heat exchanger 11 to a circulating pump 17. From the
circulating pump 17 the liquid is passed to a reservoir 20 via a line 29 and a
second return line part 16 is connected from the reservoir 20 to the heater 13
forming a closed circuit for the flow of heat exchange fluid utilized to transfer heat
from the heater 13 to the water in the tank 12.
Any suitable heat exchange liquid can be used, and in the example
illustrated the liquid used is a glycol-water mix which is preferred because it has a
relatively high specific heat, has good heat transfer properties, and will not freeze
except at extremely low temperatures.
Within the heater 13 the glycol is circulated through a coil or sinuous
20 tube bank 18 which is exposed to absorb heat created in a heating element 19,
the latter in the example illustrated comprising a Catadyne (Trademark) catalytic
building heater. The Catadyne heater produces infrared radiant energy without
flame and has proven to be reliable and safe in use. Where the heater 13 is
mounted indoors, any generated heat that is not absorbed in the coil 18 can be
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utilized to warm the interior of the building.
The circulation pump 17 is powered by pressurized propane or
natural gas from a supply 22 delivered through a line 23 and a valve 24 to the
circulation pump 17. Make-up gas from the same supply 22 can also pass from
the line 23 through a regulator valve 25 to a line 26 through which gas is delivered
to the heating element 19, in order to provide sufficient fuel gas to the heater
regardless of the pump demand.
Gas supplied to the circulating pump 17 by way of the valve 24
leaves the pump together with the now-lifted glycol, and both are delivered into the
top of reservoir 20 through the line 29. In the reservoir 20 the gas is separated
from the liquid under the influence of gravity and is delivered through a line 30 for
passage to the heating element 19 for use as fuel therein. A pressure release
valve 31 communicates with the interior of the reservoir 20 to relieve any excess
pressure that may develop therein.
The gas introduced into the pump 17 combines with the cold liquid
returning at low elevation. The combined gas and liquid are lifted to a higher
elevation into the top of reservoir 20 where they are separated from each other as
previously mentioned. The cold glycol mix is now free to flow through the rest of
the liquid circuit by virtue of the pressure head produced by its change in
20 elevation. In other words, the glycol mix in the reservoir exerts a higher static
pressure on the reservoir bottom outlet line 16 than that found at the pump suction
line 15. From the reservoir the cold glycol mix reaches the coil 18 and is heated
as it passes through. From there, the liquid flows out line 14 to the heat
exchanger 11. As it passes through the exchanger, heat is lost from the glycol
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mix transfer fluid and gained by the tank contents 12. Alternatively, the tank may
be replaced by any other device or piping system requiring heat. From the
exchanger 11, the cold liquid flows back to the pump suction via line 15,
completing the circuit. It is evident that the flow is also assisted by the natural
convection currents which develop as a result of the temperature gradient between
the heating coil 18 and the tank exchanger 11.
As mentioned, the pump 17 is of a type that does not require a motor
for its operation, but rather is one that can be powered simply by the pressure of a
gas, and one simplified pump 17a is schematically illustrated in Figure 2a as
10 comprising an open top column 35 having at its lower end (Elevation A) an inlet
port 36 connected to a supply of liquid under hydrostatic head (as from the line
15) such that the liquid will find a level 38 (Elevation C) in the column 35
according to the hydrostatic head. Above the lower port 36 at Elevation B is a
second port 40 to which gas under pressure regulated by the valve 24 can be
delivered. It will be appreciated that gas injected through the port 40 will tend to
move upwards through the column and to raise the liquid which lies above it in the
column. It will be understood that as gas rises in the column 35 slugs of liquid
above it are lifted vertically to a height (Elevation D) above the point of gas
introduction (depending on the column diameter, liquid velocity, gas pressure, gas
20 volume, hydrostatic head etc.) which results in a pumping action, and the gas can
be supplied more or less continuously.
The alternative pump 17b shown in Figure 2b is modified from the
one shown in Figure 2a by the inclusion of a piston 41 within the column above
the second port, the piston 41 being slidable vertically within the column. In this
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embodiment the pressurized gas is not introduced continuously through the port
40, but rather is introduced in pulses of a given volume, pressure, and rate. The
piston 41 is forced to move upwardly when a charge of compressed gas is
introduced beneath it, so that the liquid above the piston is pumped upwardly.
When the gas supply is cut off after a predetermined time, gas in the column
beneath the piston can leak upwardly past it, and the piston will subside to its
starting position just above the port 40, whereafter further charge of gas can be
admitted. The piston can take various forms: as illustrated in Figure 2b, the
piston 41a being solid and loose fitting within the column 35; the piston 41b being
10 of inverted cup shape and having an orifice 42 at its upper end through which gas
and liquid can pass upwardly as the piston returns to its starting position; and at
41c a loose fitting piston which includes a flexible seal 43 past which gas can
escape upwardly to allow the piston to settle back to its starting position.
In the other alternative gas lift pump illustrated in Figure 2c the
column 35 is branched, the branch 47c being connected to the gas supply which
is delivered under regulated pressure and volume in pulses under the control of a
timer (not shown). When a pulse of pressurized gas is delivered it will force the
liquid from the branch 40c into the column 35. A check valve 36a provided in the
liquid supply prevents backflow of liquid so that the displaced liquid is forced
20 upwardly in the column 35 in a pumping action. When the gas pulse is dissipated,
a fresh supply of liquid will re-enter the pump through the check valve 36a rising
again to the level 38 both in the column 35 and in the branch 40c.
While presently preferred embodiments of the invention are described
above in relation to the accompanying drawings, it will be appreciated that the
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invention is capable of numerous modifications in the details thereof, and all such
are intended to be comprehended within the scope of the attached claims.
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