CA1076820A

CA1076820A - Method and apparatus for drilling a hole in a body of ice and for the destruction of a body of ice

Info

Publication number: CA1076820A
Application number: CA284,701A
Authority: CA
Inventors: Robert M. Hopkins; Roger C. Parsons
Original assignee: Resource Development Consultants Ltd
Current assignee: Resource Development Consultants Ltd
Priority date: 1977-08-15
Filing date: 1977-08-15
Publication date: 1980-05-06

Abstract

ABSTRACT OF THE DISCLOSURE

A method and apparatus for drilling a hole in a body of ice and for destroying a body of ice. The method comprises the steps of providing a source of reactant gas of a type which will react chemically with ice to form solid compounds which are unstable and which break down rapidly to water and a dissolved gas. The reaction product which is formed is removed quickly in order to avoid a secondary and initially undesirable exothermic reaction of gas dissolution into the water so formed. The reactant gas is directed through a nozzle to generate a stream of reactant gas. The nozzle is located in close proximity to a body of ice, and the stream of reactant gas is directed against a localized area of the surface of said body of ice at a velocity and flow rate to obtain an optimum phase change reaction with the ice and to quickly remove water formed from the ice in the localized area. The nozzle is advanced towards the body of ice to continue to direct the stream of reactant gas against the receding surface of the body of ice in the localized area as the ice undergoes a phase change to the liquid state to destroy the body of ice or to form a hole in the localized area in the body of ice.

Description

~ 68~0 FIELD OF INVENTION

This invention relates to a method and apparatus for destroying a body of $ce and for drilling a hole $b a body of ice.
PRIOR ART
Conventional methods fall into two categories, namely, mechanical methods and thermal methods.
Mechanical methods of drilling a hole in a body of -ice include the use of a drill or auger which is rotatably driven into the body of ice. The apparatus required in order to drill a hole in ice ls cumbersome and difficult to operate, particularly under Arctic conditions~ In addition, the drilling tool must be replaced or sharpened at frequent inter-vals and the servicing of the drilling tool and other mechanical components is difficult under adverse weather conditions.
Thermal processes for destroying a body of ice and drilling a hole in ice operate on the bas~s of transferring heat to the ice tu supply enough energy to convert the ice from the solid to the liquid phase and to maintain it in the

2~ liquid phase. Examples of such systems are well known and include apparatus designed to deliver steam jets or hot water - jets. These systems have a high heat requirement and make a very inefficient use of the heat which is supplied. They are inherently slow because heat has to be transferred through a liquid film on the ice surface.
Dry thermal systems such as heated rods have also been used to form a hole in a body of ice. The heated rod system operates very slowly and is not considered to be practical for the vast ma~ority of commercial applications.
A method of removing ice from the windshield of an automobile or the like is described $n ~.SO Patent 33776,775.

107~8~0 The system disclosed in this patent provides a source of two dissimilar chemical compositions which react with one another to produce a high temperature fluid which is then directed against the surface of the ice to melt the ice. The two compositions are stored in two separate compartments in a dispenser container and are only mixed when dispensed there-from. The two compositions must be carefully formulated and carefully mixed at the nozzle to obtain the required generation of heat. Thus, in this known system heat is generated as soon as the apparatus is activated to discharge the compositions therefrom. The system is, therefore, a self-sustaining thermal system which provides a source of heat capable of melting ice.
The present invention overcomes the difficulties of the prior art described above and provides a simple and efficient method for destroying a body of ice wherein the ice itself reacts chemically with a stream of gas directed against a locali7ed area thereof. In this method the gas is of a type which will react chemically with ice to form unstable compounds which immediately revert to water and dissolved gas but will not react to generate heat until it ma~es contact with the ice or water.
SUMMARY OF INVENTION
AccDrding to one aspect of the present invention, there is provided a method of destroying a body of ice and for drilling a hole in a body of ice which comprises the steps of: providing a source of reactant gas of a type which will react chemically with ice to form unstable compounds which immediately revert to water and dissolved gas; directing said reactant gas through a nozzle to generate a stream of reactant gas; locating said nozzle in close proximity to a body of ice;

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768'~0 directing said stream of gas against the surface of said body of ice at a velocity and flow rate to obtain an optimum solid to liquid phase change reaction with the ice; immediately removing the water formed from the ice and the dissolved gas and advancing the nozzle towards the body of ice to continue `~
to direct the stream of reactant gas against ehe receding surface of the body of ice to destroy the ice.
According to a further aspect of the present invention, the reactant gas may be selected from the group consisting of ammonia, hydrogen chloride, sulphur dioxide or ~;
ammonium chloride above its dissociation temperature of 340 , or other gases which fall within the following classes of chemicals : ammonium salts of the Halogens, Halogen Acids, ~;
Ammonium Salts of Sulfur~ Oxygen Acids~ and Oxides of Sulfur.
All the above reactant gases will react with ice to form an unstable compound where the end products formed have the property that the summation of their energies, forming the Gibbs free energy, is negative.
The invention will be more clearly understood after reference to the following detailed specification read in conjunction with the drawings wherein, Fig. 1 is a diagrammatic illustration of an ice drilling devicP according to an embodiment of the present invention;
Fig. 2 is a diagrammatic representation of an ice drilling mechanism according to a further embodlment of the present invention;
Fig~, 3 is a diagrammatic view of an ice drilllng mechanism according to a still further embodiment of the present invention;

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10'76~ 0 Fig. 4 is a graph showing ice destruction rate as a function of ammonia flow rate for various nozzles; and Fig. 5 is a graph showing the thermodynamic efficiency as a function of ammonia flow rate for various nozzles .
With reference to Fig. 1 of the drawings, a drill rod 10 is shown to be connected to a gas storage tank 12 by means of a flexible conduit 14. A pressure flow volume control valve 16 is provided in the line connecting the conduit 14 and container 12. A drill rod guide 18 is provided for guiding the drill rod axially towards a body of ice 20.
The drill rod 10 is in the form of a hollow tubular member and has a nozzle 22 located at one end thereof. The container 12 contains a supply of a reactant gas from the following classes of chemicals: Ammonia, Ammonium salts of the Halogens, Xalogen Acids, Ammonium Salts of Sulfur, Oxygen Acids, and Oxides of Sulfur which reacts with ice to generate unstable compounds which in turn break down into a solution -of the reactant gas in water. A heating element 15 is wound around the container 12 and serves to heat the container as the reactant gas is discharged therefrom to maintain the required vapor pressure and thereby the flow. Examples of suitable reactant gases are ammonia, hydrogen chloride, sulphur dioxide and ammonium chloride, above its dissociation temp-erature. The latter will also be a suitable reactant if heated as described below with reference to Fig. 3.
The drill rod guide 18 consists of a tripod frame 24 having upper and lower guide rings 26 and 28 having passages 30 and 32 opening therethrough for guiding the drill rod vertically into the body of ice in use.

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Fig. 2 of the drawings illustrates a modified apparatus in which storage containers 12a and 12b are provided.
The storage container 12a has a control valve 16a and the storage coDtainer 12b has a control valve 16b. Conduits 14a and 14b connect the control valves 16a and 16b to a drill rod lOa which has coaxial passages lla and llb extending there-through. The passage llb is connected to conduit 14b and the passage lla is connected to conduit 14a. The nozzle 22 has a through passage 22a which communicates with the passage lla of the drill rod and a passage 22b which communicates with the passage llb of the drill rod. In this apparatus, the container 12a may contain a reactant such as ammonia and the container 12b may contain an inert gas such as nitrogen, the ammonia and inert gas being mixed at the discharge end of the nozzle 22. It will~ however, be noted that the mixing of the two gases does not result in a chemical reaction.
Fig. 3 illustrates a further system according to an embodiment of the present invention in which an inert carrier gas from a source 34 is conveyed to a heat exchanger 13 by conduit 14c. The carrier gas is conveyed from the heat exchanger 13 by conduit 14d to a source 12d which may contain a reactant such as ammonium chloride ~NH4CL)~ Dissociated ammonium chloride mixed with the carrier gas is conveyed to a drill rod by way of conduit 14e~
In use, a stream of reactant gas impinges on a localized arel of the surface of a body of ice. The reactant gas absorbs on the surface of the ice forming an unstable product which dissociates into a solution of the reactant gas in water.
The mechanism whereby ice is melted with soluble gases, using ammonia as an example, is considered to be as follows :

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When anhydrous ammonia is impinged upon ice, two ammonia hydrates are formed, namely NH3.H20 and 2NH3.H20. At :
temperatures above 194K (-79C) both of these compounds are unstable and decompose into a complex mixture of ice (H20( ))~
water (H20~1)) dissolved ammonia (NH3(aq~), gaseous ammonia (NH3(g)), ammonium ions (NH4+) and hydroxyl ions (OH~
Contraty to general belief, undissociated ammonium hydroxide (NH40H) has not been shown to exist in aqueous solution, and equilibrium data shows that NH4+ and OH- can exist only in very small amounts. The equilibrium constant for the reaction NH3(aq) + H20(l)~ > NH4+ + OH
is K = LNH4+]~OH-] = 1.81 x 10 5 : NH3 Hence when ammonia is impinged on ice, depending upon the temperature of the system~ the main reactions governing the process are considered to be as follows : :

NH3(g~ + H2o(s)~NH3-H2o(s) ,~ `
2NH3(g~ + H20(S)~2NH3-H2 (s) NH3-H2(s)'~ ) H20(1) + NH3(aq) 2NH3-H2o(s)~ ~ 2 (1) 3 : 3(g) ~ 2 (1) 3( q) In essence, these reactions mean that if anhydrous ammonia is impinged on ice at a temperature above 194K the Eollowlng seqtence oE events occur.

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H3(g~ ~ ~

Impingement Formation of Formation of Phase changes of of gas NH3 2 (s) 3(aq)+ H2(l) reaction products Step 4 represents the changes that the reaction 10 products can undergo. These are highly temperature dependent, since ice can be reformed according to the equilibrium between ice and water.
H20(1)s__~H20(s) (temp. dependent) Am~onia can re-enter the vapour phase according to the reaction NH3(aq)~=~NH3(g) (temp.and pressure dependent) Depending on conditions of te~perature and pressure, ammonia can enter the liquid phase and because of the heat of dilution involved result in the melting of ice by thermal heat transfer process. However, such a process is initially highly undesirable --~ 20 as the thermal conductivity of aqueous NH3 solutions is very low 8.2676 x 10 CAL./sec. - cm~ - C (0.2 BTU/ft - hr - F) and the melting rate very slow. Consequently this reaction competes for ammonia with the main reaction of the process (the formation of unstable NH3.H20 and 2MH3.H20) and as a ~?
result is iDitially undesirable in that the dilution ~an take place between the nozzle and the receding ice surface utilizing the water formed from the break down of the unstable compounds and the ammonia gas being supplied. It is by this method that . ' '' .
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the secondary reaction (i.e. dilution) competes for ammonia and reduces the effectiveness of the device. Once the liquid melt water resulting from the break down of unstable compounds has been quickly removed from the interface between the nozzle and receding ice surface~ this secondary reaction is supplementary in that it destroys ice by thermal process as it moves away from the interface while not competing with the prime reaction (i.e. formation of unstable compounds~. This maximizes pene-tration rate (controlled by formation of unstable compounds) and destruction rate (controlled by formation of unstable com-pounds and supplemented by thermal processes).
Steps are thus taken to avoid the secondary dilution reaction at the interface (between nozzle and receding ice surface). These are:
1) using NH3 gas velocities up to the speed of sound to remove the aqueous phase from the surface of the ice as quickly as pDssible.
2) combining the ammonia with an inert gas such as nitrogen to serve as a vehicle for removal of the aqueous phase.
The drilling process does not cause elevated tempera-tures of any of the components. It is essentially an isothermal process and does not rely on the creation of a thermal gradient between a liquid and the ice surface. It relies on a phase ` change of the ice to the liquid phase via the formation of the unstable compound NH3.H20 and 2NH3.H20. By this method the ` inefficiency inherent in current methods that of the slowness of heat transfer through a water media is avoided.
' The apparatus of Fig. 1 would operate in accordance wlth the above system when the storage container 12 is charged with ammonia. As previously described, gases other than ammonia 1~68~3 which fall within the following classes of chemicals : A~monium Salts of the Halogens, Halogen Acids, Ammonium Salts of Sulfur, Oxygen Acids and Oxides of Sulfur, can be used in the drilling apparatus with associated advantages and disadvantages. For example, if NH4Cl is used, more ice can be destroyed per unit pass of gas. However, NH4Cl has to be volatized in the field, therefore requiring a higher capacity heat source. On the other hand NH4Cl produces a large freezing point depression (as do ; all described reactants) thereby eliminating the problem i 10 associated with refreezing.
`~ In certain applications~ it may be desirable to com-- bine the reactant with an inert gas such as nitrogen or air and this çan be achieved by means of the apparatus illustrated in Fig. 2 of the drawings.
In a system in which the reactant is ammonium chloride, for example, a heating system is required to volatize the ammonium chloride. Such a system is illustrated in Fig. 3 of the drawings wherein the carrier gas is heated in a heat exchanger before it is admitted to ehe ammonium chloride storage container. By this means HCl and ~H3 are at too high a temperature to react with each other but react directly with the ice.
Drilling tests have shown that a hole can be formed in a body of ice very efficiently by directing a stream of ammonia against a localized area of the surface of a body of ice.

107ti8~ r Test Procedure The experiments on the ice penetration syseem were conducted using four different size nozzles, ranging from a 1.0 mm diameter nozzle to a 4.0 mm diameter nozzle. For each different size nozzle flow rates from 20 L/min through 120 L/min were tested.
Then for each nozzle size and each different flow rate, a series of holes was drilled in the ice. This procedure consi~ted of drilling three holes for time periods of 5, 10.
15, 20 and 25 seconds for each flow rate. This constituted a set of readings and for each set a graph of depth drilled versus time was plotted. From these graphs drilling rateswere determined.
Immediately after the holes were drilled, they were filled with water at 0C (to prevent further melting) in order to measure the volume of ice destroyed. Then graphs of volume of ice destroyed versus time were plotted and from these ice destruction rates were obtained. This information, in conjunction with calculated the~modynamic efficiencies, supplied the necessary information to obeain the optimum operating conditions for the ice penetration systemO
A series of drilling tests were carried out using ammonia. Horizontal and vertical drillings were perfor~ed using pure ammonia and results obtained for each. From these results, drilling rates were determined using the method described above. The results of these tests were as set forth below in Table 1 and Table 2.

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10'768Z0 Table 1 -FLOW RATE HORIZO~ ITAL DRILLING ~ATES (cm/m- In) 1.O n~ 2.0 mm 3.0 mm 4.0 mm L/min (approx.) no 7. %le nozzle noz%le noz 7,1 e ___ _~ __ .__ _ _. ____ __ ___ __ _ 42 20.4 21.9 23 62.4~.2 _ 31 71.254.647.4 39 75 -86.4 _ 46 82.8 71 variable 40.2 62 _ 97 87 97.2 77 _ 144 87 11~.5 92 _ _ 99 141 - Table 2 `
I
FLOW RATE j VERT: CAL DRILLING RATE-(cm/n in) 1 0 mm 2 0 mm 3.0 mm4.0 mm L/min (approx.) I nozzle nozzle nozzlenozzle 33.4 _ _ _ i 23 _ _ _ 31 58.2 58.2 _ 22.4 39 73.2 _ _ 46 _ 72.0 73.5 40.2 `Z0 6~ l ¦ _ ¦1 a a¦ 66 0 '~ 92 _ 117 ~ 84.~

~ , 1(~76B20 Efficiency Calculation Thenmodynamic analysis of the process has shown that the energy supplied in the reaction process is converted at an efficiency of 50-60% into ice destruction (Fig~ 5).
For a 3.0 mm nozzle with ~m ammonia flow of 40 L/min Flow Rate of NH3 = 40 L/min = .064 lb m/min at STP
= 29.1 gm/min at STP
; Heat of Reaction = 29.1 gmjmin x 490 cal/gm = 14~259 cal/min Rate of Ice Destruction = 105 cm /min Heat of Fusion = 105 cm x 0.9 ~3 x 80 cal min cm gm = 7560 cal/min Efficiency = 7 560 = 53%

From the graphs previously described, the drilling rate for any specific flow rate can be obtained. Similarly a graph of volume of ice destroyed versus flow rate was obtained (Fig. 4).
This information combined with the efficiencies at different flow rates enables one to determine the optimum flow rate and nozzle size for the maximum utilization of an ammonia tank. Thermodynamic efficiency can be calculated by using the equation :

Efficiency = energy consumed in phase chan~e reactlon energy supplied by reactant From the calculated efficiencies a graph of efficiency versus flow rate was constructed (Fig. 5).
From these graphs it can be determined that in order to obtain a high drilling rate (approximately 140 cm/min)~ a 2.0 mm nozzle with an ammonia flow of approximately 80 Lfmin would be the most efficient. Similar tests can be carried out .' ~''~
~ - 12 _ ~.... . .. .....

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to determine the optimum operation conditions for the various other reactants proposed.
As previously indicated, when ammonia is used as a re-actant it may be necessary to provide a secondary heatlng system to heat the ammonia tank to maint*in the vapor pressure inside the ammonia tank. As the ammonia evaporates, it absorbs a con-siderable amount of heat from the liquid ammonia, thus reducing the temperature in the ammonia tank. If the ammonia removes too much heat, then the vapor pressure drops to an extent that the ~ ;
gas flow may not be sufficient for drilllng a~ optimum rates.
In order to solve this problem, heat is applied in a sufficient quantity to maintain the vapor pressure in the am-monia tank at a working level. ~he power required to heat the tank in order to maintain this pressure with a flow of 80 L~min is 1300 watts. However, to provide for various flow rates under working conditions and where a 15 lb. ammonia tank is to be used, the heating system should have a minimum power density of 5600 watts/m2 (2000w/surface area of 15 lb tank). If a 100 lb. tank -is used (O.D. = 12", L = 49"), the area is 1.26 m2. Thus, the power density required ls reduced to approximately 1600 watts/m2 ~2000 w/1.26 m2).
During preliminary tests, drilling was carried out with-out the aid of a rod plumbing device or guide of the type illus-trated in Flg. 1 of the drawings. In the course of these tests, it was noted that di~ficulty was experienced in attempting to keep the drill rod perpendicular to the surface of the ice.
The holes which were being drilled by manually supporting the drLll rod were 'Lnclined at an~les up to 30 from the vertical.
It is believed that thls problem was most likely due to flaws ~ust below the surface of the ice. If ~here was a cavity, crack or soft spot in the ice, the rod would tend to penetrate this 1~766~ 0 section first, thus causing the rod to move at an angle~
This problem initiates near the sur~ace of the ice with the walls of the hole formed by the drilling operation acting as a retainer to keep it at an angle. The guide mechanism illustrated in Fig. 1 of the drawings serves to overcome this problem. ~-From the foregoing it will be apparent that the present invention provides a simple and efficient system for drilling a hole in ice by chemical means. The reactant gas combines chemically and isothermally with the ice causing a phaee change to the liquid state. Nozzles can be readily calibrated to determine the most efficient flow rate and the flow of reactant through the nozzle can be regulated to provide optimum drilling efficiency.
The system of the present invention provides a simple and efficient method and apparatus for drilling a hole in ice `~
and for the destruction of a body of ice by chemical means.

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. .

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows

1. A method of destroying a body of ice comprising the steps of :
(a) providing a source of reactant gas of a type which will react isothermally with ice causing the formation of unstable compounds which immediately revert to water and dissolve gas, but will not react until it makes contact with ice or water, (b) directing said reactant gas through a nozzle to generate a stream of reactant gas, (c) locating said nozzle in close proximity to a body of ice, (d) directing said stream of gas against a localized area of the surface of said body of ice at a velocity and flow rate to obtain an optimum phase change reaction with the ice and advancing the nozzle towards the body of ice to continue to direct the stream of reactant gas against the receding surface of the body of ice as the ice changes phase.

2. A method of destroying a body of ice as claimed in Claim 1 wherein the water formed from the ice is removed from the localized area as rapidly as possible after it has been formed so that it does not prevent direct impinging of the reactant gas onto the body of ice.

3. A method of destroying a body of ice as claimed in Claim 2 wherein an inert gas is directed against the water to remove it from the localized area.

4. A method of destroying a body of ice as claimed in Claim 1, 2 or 3 wherein the reactant gas is selected from the group consisting of Ammonium salts of the Halogens, Halogen Acids, Ammonium Salts of Sulfur, Oxygen Acids and Oxides of Sulfur.

5. A method of destroying a body of ice as claimed in Claims 1, 2 or 3 wherein the reactant gas is selected from the group consisting of ammonia, hydrogen chloride, sulphur dioxide and ammonium chloride.

6. A method of drilling a hole in a body of ice comprising the steps of :
(a) providing a source of a reactant gas of a type which will react isothermally with ice causing the formation of unstable compounds which will revert to water and dissolved gas, but will not react until it makes contact with ice or water, (b) directing said reactant gas through a nozzle to generate a stream of reactant gas, (c) locating said nozzle in close proximity to a body of ice, (d) directing said stream of gas against a localized area of the surface of said body of ice at a velocity and flow rate to obtain an optimum phase change reaction with the ice and thus destroy the ice in the localized area, (e) advancing the nozzle towards the body of ice to continue to direct the stream of reactant gas against the receding ice in the localized area as the ice is destroyed to form a hole in the body of ice.

7. A method of drilling a hole in a body of ice as claimed in Claim 6 wherein water formed from the ice is removed from the localized area as rapidly as possible after it has been formed so that it does not prevent direct impinging of the reactant gas onto the body of ice.

8. A method of drilling a hole in a body of ice as claimed in Claim 7 wherein an inert gas is directed against the melt water to remove it from the localized area.

9. A method of drilling a hole in a body of ice as claimed in Claim 6, 7 or 8 wherein the reactant gas is selected from the group consisting of Ammonium salts of the Halogens, Halogen Acids, Ammonium Salts of Sulfur, Oxygen Acids and Oxides of Sulfur.

10. A method of drilling a hole in a body of ice as claimed in Claim 6, 7 or 8 wherein the reactant gas is selected from the group consisting of ammonia, hydrogen chloride, sulphur dioxide and ammonium chloride.

11. A method of destroying a body of ice comprising the steps of :
(a) providing a source of reactant gas selected from the group consisting of ammonia, hydrogen chloride, sulphur dioxide and ammonium chloride will react with ice to affect a rapid breakdown of the ice, (b) directing said reactant gas through a nozzle to generate a stream of reactant gas, (c) locating said nozzle in close proximity to a body of ice, (d) directing said stream of gas against a localized area of the surface of said body of ice at a velocity and flow rate to obtain an optimum reaction with the ice and thereby affect a rapid breakdown of the ice.

12. A method of destroying a body of ice or the like as claimed in Claim 11 wherein the reactant gas is selected from the group consisting of Ammonium salts of the Halogens, Halogen Acids, Ammonium Salts of Sulfur, Oxygen Acids and Oxides of Sulfur.

13. A method of destroying a body of ice as claimed in Claim 12 wherein the reactant gas is selected from the group consisting of ammonia, hydrogen chloride, sulphur dioxide and ammonium chloride.

14. A method as claimed in Claim 1, 2 or 3 wherein nitrogen is mixed with the reactant gas at or prior to discharge from the nozzle.

15. A method as claimed in Claim 6, 7 or 11 wherein nitrogen is mixed with the reactant gas at or prior to discharge from the nozzle.

16. A method as claimed in Claim 1 or 6 wherein the reactant gas is discharged through a 2 mm nozzle at a flow rate of 80 L/min as the nozzle is advanced towards the receding surface of the localized area at a rate of 140 cm/min.

17. An apparatus for drilling a hole in a body of ice comprising :
(a) a source of reactant gas of the type which will react with ice to breakdown the ice, (b) a hollow drilling rod having a nozzle at one end thereof, (c) conduit means connecting said hollow drilling rod with said source of reactant gas, and (d) means for regulating the flow of reactant gas through the nozzle to control the flow rate and velocity of the stream of gas to obtain an optimum chemical reaction with ice as the nozzle is advanced into a body of ice to form a hole.

18. An apparatus as claimed in Claim 16 including heater means for heating said source of reactant gas.