GB2284203A - Removal of gases from flue gases - Google Patents

Abstract

A process for the removal of carbon dioxide and other environmentally damaging gases from the flue gases of electrical power generating stations in which the gases are reacted with dolomite suspension. <IMAGE>

Description

A Process for the Removal of Carbon Dioxide from the Flue Gases of Electrical Power Generating Stations Introduction.

Carbon dioxide gas is produced naturally by animal respiration, from the decay of plant and animal material and from volcanoes. The gas is used by plants, which return oxygen from the carbon dioxide to the atmosphere for use by oxygen dependent life forms. This is a simpified version of the natural carbon dioxide gas cycle. Human activity has added another non natural component to this cycle by producing carbon dioxide gas from systems designed to obtain useful energy, particularly electrical and transport energy, and also to obtain products not available naturally. This addition has been made continuously since the industrial revolution first started in the United Kingdom two hundred years ago. There is now evidence that the amount of carbon dioxide in the atmosphere is rising as a result.

This situation is novel to the human race and the there have been various predictions as to the consequences of the rise. There is however a concensus that the effects of the rise are unlikely to be entirely beneficial and efforts are now being expended to reduce the amount of carbon dioxide that will be added to the atmosphere in the future. The process described below is capable of removing carbon dioxide gas from the flue gases of elecrical power generating stations and converting it to a form which allows safe disposal or use without detriment to the environment of the planet Earth.

The Process for the Capture and Disposal of Carbon Dioxide Gas from Power Stations.

The process is based on the use of the natural mineral dolomite which is a mixed compound of magnesium and calcium carbonates. Magnesium carbonate is not particularly soluble in water in the absence of carbon dioxide gas. The value of the solubility being of the order of 0.2 grams per litre. However when carbon dioxide gas is passed through a suspension of magnesium carbonate in water saturated with carbon dioxide and with one atmosphere pressure of carbon dioxide gas above the suspension, the solubility markedly increases as shown graph 1.

Magnesium carbonate dissolves to give a clear solution known in industry as fluid magnesia. It is supposed that the soluble compound formed is magnesium bicarbonate [Mg(HCO3)2] although this compound has never been isolated as a solid. The relevant chemical equation is: MgCO3 + CO2 + H20 - Mg(HCO3)2 The same is true for calcium carbonate with the difference that the amount of this compound that dissolves is very much less, about five percent of the amount of magnesium carbonate that dissolves under the same conditions. The amount of magnesium carbonate that can be dissolved in a given amount of water is dependent on the pressure of carbon dioxide gas used as shown by graph 1. The solution of magnesium carbonate in water saturated with carbon dioxide is not stable and if the partial pressure of carbon dioxide in the atmosphere above the solution falls below 0.02 atmospheres then all the carbon dioxide will be lost and the magnesium carbonate will reappear as a solid. The partial pressure of carbon dioxide in the normal atmosphere is 0.00028 atmospheres. Thus although the above reaction is a means of removing carbon dioxide from flue gases of a power station the solution would commence to decompose and release carbon dioxide within hours of formation when exposed to normal atmosphere, Magnesium carbonate also dissolves in sodium chloride solution. In the absence of carbon dioxide the solubilty is again low and at first increases and then decreases in the the presence of sodium chloride as the concentration of the latter is increased (graph2). The amount of magnesium carbonate that dissolves in a solution of sodium chloride under one atmosphere pressure of carbon dioxide gas is greater and is nearly constant until the amount of sodium chloride reaches a particular value. After this point the solubility rapidly falls (graph 3). This leads to the conclusion that a change in the compounds in the solution takes place at this point. It is proposed that magnesium carbonate dissolves in an aqueous solution of sodium chloride in the absence of carbon dioxide gas as the normal carbonate and in the prescence of carbon dioxide as magnesium bicarbonate. At the point of change (graph 3) magnesium carbonate dissolves in the sodium chloride solution as the result of the formation of sodium bicarbonate and magnesium chloride.

MgCO3 + C02 + H20 + 2NaCI c Mg(HCO3)2 +2NaCI o 2NaHCO3 + MgC12 The continued decrease in the solubility of magnesium carbonate with increasing concentration of sodium chloride results from the fact that the solubility of sodium bicarbonate in water is decreased by the presence of sodium chloride. The graphs 4 and 5 shows that a concentration of 360 grams per litre of sodium chloride reduces the solubility of sodium bicarbonate by a factor of eight over a range of temperatures. The solubility of any sodium bicarbonate formed by the above reaction will be reduced by an increasing excess of unreacted sodium chloride.

This limits the amount of sodium bicarbonate that forms and dissolves and in turn reduces the amount of magnesium carbonate that dissolves.

This can be demonstrated by the figures given in graph 3 where the results are for a temperature of 23"C. At the point of change 30.6 grams of magnesium carbonate dissolve in one litre and would produce 53.1 grams of magnesium bicarbonate. This in turn would react with 42.4 grams of sodium chloride and form 60.9 grams of sodium bicarbonate leaving 14.1 grams of sodium chloride per litre.

This will reduce the solubility of sodium bicarbonate, however the effect is not sufficient to reduce the solubility from the value in pure water of 96 grams per litre (graph 5) to below 60.9 grams per litre and the sodium bicarbonate formed will not precipitate. At the level of 306.6 grams of sodium chloride per litre in contact with magnesium carbonate suspension only 10.75 grams of magnesium carbonate dissolve per litre (graph 3). This amount would produce 21.4 grams of sodium bicarbonate and represents the amount of sodium bicarbonate that can dissolve in the sodium chloride solution of a concentration of 299.1 grams per litre remaining after the sodium bicarbonate has formed. The value for the solubility of sodium bicarbonate in sodium chloride in a concentration of sodium chloride 360 grams per litre in the abscence of magnesium chloride is 13 grams per litre from graph 2 at the same temperature of 23"C. These results are sufficiently close to indicate that the conclusion that magesium carbonate dissolves in concentrated sodium chloride solution as the result of the formation of sodium bicarbonate is likely to be correct. The values given in graph 3 allow the calculation of the the reduction in the solubility of sodium bicarbonate in the prescence of the concentration sodium chloride after the reaction with magnesium carbonate is complete.. The results are presented in graph 6. Based on these results when a solution of magnesium carbonate in water containing 30.6 grams per litre under one atmosphere pressure of carbon dioxide is stirred with 360 grams of solid sodium chloride about 20 grams of the magnesium carbonate will precipitate and carbon dioxide gas will be released. This conclusion is valid provided the pressure of carbon dioxide is not allowed to increase. By increasing the pressure of carbon dioxide in contact with water increases the amount of magnesium carbonate that can dissolve (graph 1 ).

Hence increasing the pressure of carbon dioxide over a solution of sodium chloride contact with a suspension of magnesium carbonate in a closed system would be expected to increase the amount of sodium bicarbonate formed.

In principle by arranging conditions where the solubility of the magnesium bicarbonate is greater than that of sodium bicarbonate in a solution of sodium chloride the above proceedure will result in the precipitation of sodium bicarbonate. This process being aided by the reduction of the solubility of sodium bicarbonate in the presence of sodium chloride.

In the last half of the nineteenth century W. Weldon proposed that this conclusion be used to produce sodium bicarbonate industrially. The chemical reaction given above would be expected to be reversible controlled by the carbon dioxide pressure. Increases in carbon dioxide pressure would normally drive the above reaction to produce the products on the right hand side of the equation according to the principle of Le Chatelier.The thermal value of the above reaction is -37.49 KCal indicating that it is exothermic. An increase in temperature has been noted when calcium carbonate dissolves in water saturated with carbon dioxide.

This means that as the reaction proceeds the solution will increase in temperature and the solubility of the magnesium carbonate will decrease as shown in graph 6 and this compound will be precipitated. From the data on graph 1 the amount of magnesium carbonate that dissolves in a litre of water at 10 atmospheres pressure of carbon dioxide is 60 grams per litre producing 104 grams of magnesium bicarbonate. If 360 grams of sodium chloride are stirred into this solution the magnesium bicarbonate will react with 83.1 grams of the sodium chloride and produce 119.4 grams of sodium bicarbonate. The amount of sodium choride left is 276.9 grams and at normal pressure this reduces the solubility of sodium bicarbonate to 22.9 grams per litre (graph 6). Under these circumstances is it to be expected that 96.5 grams of sodium bicarbonate will precipitate provided the temperature is not allowed to rise. In the absence of the excess sodium chloride only 23.4 grams of sodium bicarbonate would precipitate.

The above reaction will occur provided there are no other complex compounds that can form and precipitate.The sodium equivalent of the Engel Precht potassium salt (KHCO3MgCO34H2O) would be formed by the reaction 3(MgCO33H2O) + 2NaCI + C02 +H20 = MAC12 + 2(NaHCO3MgCO34H20} From this equation 41.4 grams of magnesium carbonate per litre are required to be dissolved along with 11.7 grams of sodium chloride per litre. This amount of magnesium carbonate will not dissolve in a litre at normal pressure of carbon dioxide and requires a pressure of 5 atmospheres. However the amount formed (48.1 grams per litre) does not necessarily exceed the solubility of the complex compound.

There also exists a complex magnesium chlorocarbonate [Na3(MgCl)(CO3)2] that could form and precipitate. Sodium bicarbonate in solution is hydrolysed and the prescence of carbon dioxide under pressure could to lead to the reaction MAC03 + 2NaCI + cm2 + H2O = 2NaHCO3 + MgC12 4NaHCO3 + 4H2O + MAC12 = 4H2CO3 +4NaOH + MgC12 = 2Na2CO3 + H2O + H2CO3 + MgCI2 + NaCI = Na3(MgCI)(0O3)2 + 2NaCI This sequence of reactions are therefore a possible source of the complex carbonate.The compound precipates from a heated solution containing 27 grams of magnesium chloride, 36 grams of anhydrous sodium carbonate per litre and 273 grams of sodium chloride per litre of water. The sodium chloride is clearly in excess of the amount required to form the complex carbonate and and this indicates that the prescence of excess sodium chloride in solution encourages the formation of this compound. From the data given above for the formation of the compound the solubility can be estimated at 70.4 grams per litre. However in the process envisaged the solution is to be kept cool and the conditions under which the above compound could form are avoided. A second complex carbonate the sesquicarbonate (Na2CO3.NaHCO3.2H2O) exists and which occurs naturally as the mineral trona. The crystallisation of this compound is also encouraged by the prescence of sodium chloride and has a solubility of 2.9 grams per litre of water.

However this compound is a hydrate which will form only on crystallisation through the lowering of the solution temperature and is considered the least likely to form under the above conditions proposed for the precipitation of the bicarbonate.

The Operation of the Process The following description of the operation of the process is based on the precipitation of sodium bicarbonate under the conditions specified. The process will be essentially the same for any of the other compounds that can be formed and precipitate, as well as, or in place of, sodium bicarbonate. A flow chart of the process is given in Figure 1.

The fuel consumption of a 500 Megawatt electrical power station boiler is 200 tonnes per hour burning bituminous coal containing 18.5 % ash and 8.0% moisture.The theoretical air requirement is 1644 tonnes per hour carrying 345 tonnes of oxygen which produces 474 tonnes of carbon dioxide. It is normal to use a 20% excess of the theoretical air required for carrying the powdered coal into the burners and this makes a total exit volume of 2102 tonnes of gas per hour at a temperature of 300 C. From the densities and fractions of the gases leaving the power station burner the volume of gas is calculated as 1550 million litres per hour (C02=240 million litres, N2=1263 million litres, 02=47 million litres).The flue gases contain sulphur dioxide, nitric oxide, and some hydrochloric and hydrofluoric acid gases.

The source of magnesium carbonate is the natural mineral dolomite which a double carbonate of magnesium and calcium.

MgCO3CaCO3 ( untreated dolomite) + C02 [10 atmospheres, temperature 15"C] + H2O = [ Mg(HCO3)2, in solution] + [ CaC03, solid residue] The dolomite is suspended in water and the carbon dioxide is passed through the suspension to form the magnesium bicarbonate solution. This process requires knowledge of the rate of dissolving of the magnesium carbonate component of the dolomite in water saturated with carbon dioxide. The rate of dissolving of magnesium carbonates in water saturated with carbon dioxide at normal pressure has been observed to be dependent on the type carbonate involved normal, hydrated or basic. The time to attain the maximum solubility in the case of normal magnesium carbonate (MgCO3) has been measured at one hour.

Information available on the rate of dissolving of magnesium oxide in water saturated with carbon dioxide at normal pressure shows that a given weight magnesium oxide requires 25 minutes to dissolve in the appropriate amount of water to produce a saturated solution of the bicarbonate at a temperature of 18'C.

The solution has to be continuously stirred and with a constant flow of carbondioxide. From these values it is taken that at least one hour is required to complete the dissolving of any given amount of dolomite in water saturated with carbon dioxide.

The volume of gas produced per hour is 1550 million litres and the partial pressure of carbon dioxide in the mixture is 0.16 atmospheres. The hourly production of 474 tonnes of carbon dioxide requires 908 tonnes of magnesium carbonate and this is present in 1995 tonnes of dolomite. The amount of magnesium bicarbonate produced is 1574 tonnes. This amount of magnesium bicarbonate requires the use of 5436 tonnes of sodium chloride to produce sodium bicarbonate. Of this weight of sodium chloride 1191 tonnes react leaving 4245 tonnes and produce 1713 tonnes of sodium bicarbonate and of this 442 tonnes will remain in solution and 1271 tonnes will precipitate. Also produced are 970 tonnes of magnesium chloride which remains in solution. The volume of solution required to dissolve the above amount of magnesium carbonate is dependent on the pressure of operation and in this case the chosen pressure is 10 atmospheres (147 psi). The solvent to be used is sea water which contains 26.9 grams of sodium chloride per litre. Such a concentration of this compound will not significantly reduce the solubility of the magnesium bicarbonate as the graphs show. Calcium bicarbonate is also formed by the dissolving of calcium carbonate during the above process. However the solubility of the latter compound is only five percent of that of magnesium carbonate and the solubility is also reduced by the prescence of sodium chloride in the solution. The same is true for the formation of iron (ferrous) bicarbonate from iron impurity in the dolomite under the above conditions.

The first stage of the process is to separate the carbon dioxide from the other flue gases. This is achieved by using it to convert magnesium carbonate in dolomite to soluble magnesium bicarbonate. The flue gases are cooled by passing them through tanks into which is sprayed the sodium chloride solution from the reaction stage of the process where the heat carriedby the gases is used to evaporate the water to recover sodium chloride. The acid gases mentioned above will dissolve and as a result there will be no need for the present flue gas desulphurisation units.

The solubilty of magnesium carbonate in water saturated with carbon dioxide at the partial pressure of carbon dioxide in the gas stream of 0.16 atmospheres is 9.0 grams per litre (graph 2). This is increased to 26 grams per litre at one atmosphere partial pressure of carbon dioxide obtained by increasing the pressure of the flue gases in the next spray tower of the system r to 6 atmospheres (88 psi). The rate of liquid through the spray jets has to be 35 million litres per hour (9.7 cubic metres per second) carrying 33 grams of solid dolomite per litre (0.033 tonnes per cubic metre).Pumping speeds of 52 million litres per hour (14.4 cubic metres per second) are available from standard power station pumps with a power rating of 3.4 Megawatts and the spray rate needed above is therefore possible using one such pump for this stage of the process. A reservoir of the dolomite solution of 200 million litres (200,000 cubic metres ) will be required to give three hours reserve supply while the first hour of solution is being processed. The tank size for this is 80 metres diameter and 50 metres high. The carbon dioxide and any of the the acid gases which passed the flue gas cooling stage will dissolve at this stage.The gases which are not absorbed consisting of nitrogen and oxygen and some carbon dioxide from the reaction of any acid gases with the dolomite suspension are released to the atmosphere.

The the solution formed is passed through sprays in next tower in which the pressure is reduced to less than 0.02 atmospheres and the 240 million litres of carbon dioxide released per hour (66.7 cubic metres per second) is pumped to a holding tank. The holding tank for carbon dioxide is required to hold twelve hours of carbon dioxide production at 10 atmospheres (147 psi) pressure. The volume of this tank is 288 million litres and the dimensions are 80 metres in diameter and 60 metres high. The stripped dolomite solution in which the magnesium carbonate will have precipitated is returned to the dolomite reservoir requiring another pump of the above capacity and power rating. To pump the carbon dioxide into the holding tank at the required pressure will require a single compressor unit capable of compressing 240 million litres per hour (66.7 cubic metres per second). The power rating of such a unit is of the order of 20 Megawans. A calculated temperature rise of 205 C will be experienced during the gas compression. This gives a heat production of 6.7 x 1010 Joules per hour and a cooling circuit containing sodium chloride solution from the the evaporator tank where the flue gases are cooled is used to cool the gas (not shown in Figure 1). This provides futher heat for this evaporation process.

The second stage of the process is the reaction to produce solid sodium bicarbonate. The rate of usage of carbon dioxide is 240 million litres per hour and this is now transferred from the holding tank into the reaction chamber.The selected operating pressure is 10 atmospheres. At this pressure the solubility of magnesium carbonate is 60 grams per litre and the volume of sea water required is 15.1 million litres (15,100 cubic metres). This volume contains 1995 tonnes of dolomite or 132.1 grams per litre (0.132 tonnes per cubic metre). This is withdrawn from a second dolomite suspension holding tank containing three hours supply or 50 million litres. The tank size is 50 metres high and 40 metres in diameter. By pumping 240 milion litres of carbon dioxide gas into a tank with a free space volume of 24 million litres the required pressure is obtained. With the liquid volume used the total tank volume is 39.1 million litres and the tank size is 30 metres diameter and 50 metres high.

The reaction tank is fitted with an internal circulation system consisting of a pump which draws gas from the atmosphere above the liquid and circulates it through the liquid. This gas circulation also stirs the liquid. The tank is also fitted with a cooling unit immersed in the liquid. This unit is part of the same cooling circuit used to cool the carbon dioxide in the holding tank (not shown in the Figure 1). The reaction temperature is controlled at 15 C. During the reaction stage the carbon dioxide dissolves and the partial pressure of this gas will fall. The final pressure has to be sufficient to ensure that the solubilty of the magnesium carbonate is higher than that of the sodium bicarbonate. As the carbon dioxide dissolves the pressure is maintained above the solution at 10 atmospheres by pumping more carbon dioxide from the holding tank. This part of the process will require a period of two hours during the start up cycle and one hour thereafter because 240 million litres of carbon dioxide gas remain in the reaction tank at the end of each reaction cycle. The required sodium chloride is injected into the solution as a slurry in the least amount of sea water of one million litres (100 cubic metre ). Since the solvent used is sea water the 15.1 million litres in the reaction tank already contain 406 tonnes of sodium chloride and therefore 5030 tonnes have to be added. The reaction mixture is stirred for 30 minutes using the internal gas circulation unit.

The third stage of the process is the separation of the solid products which are calcium carbonate and sodium bicarbonate. This is achieved by filtering the liquid aided by the gas pressure in the tank. The concentrated sodium chloride solution containing magnesium chloride is transferred to an evaporation tank to recover the unused sodium chloride as a solid. The precipitate is removed from the tank by pumping as a slurry in the minimum sea water of about one million litres to a settling tank capable of holding twelve hours of production of solid product and therefore has the dimensions 10 metres in diameter and 40 metres high. This part of the process is considered to require 30 minutes. At the end of the cycle the reaction tank contains 240 million litres of unused carbon dioxide. The solution after the reaction contains 4245 tonnes of sodium chloride, 442 tonnes of sodium bicarbonate and 970 tonnes of magnesium chloride. At his stage of the process reaction solution can be returned to the reaction chamber, and the cycle repeated by adding 1191 tonnes of sodium chloride to the solution and withdrawing the carbon dioxide from the reservoir. However the increasing concentration of magnesium chloride will ultimately limit this procedure.The solubility of this compound in water is 543 grams per litre and assuming that it is the same in sodium chloride solution the limiting amount is 8200 tonnes. At the rate of 970 tonnes per hour this limit would be reached after nine cycles and the solution would have to be treated. Therefore the preferred operation is to change the reaction solution after each cycle and evaporate the spent reaction solution to recover the sodium chloride as a solid. Refilling the reaction tank is considered to require 30 minutes and the total reaction time is three hours.

Initially 5436 tonnes of solid sodium chloride have to be available from stock and thereafter the concentrated sodium chloride solution from the reaction will be the source of this compound plus additions from stock. The stock is obtained from sea water by evaporation using the waste heat of the power station. The theoretical heat out put of a 500 megawatt power generating unit is 5160 Gigajoules of heat per hour (one Gigajoules equals 1000 million Joules) and the electrical output is equivalent to 1800 Gigajoules per hour representing a 32% efficiency. The above power station power station operates two independent closed circuit heat transfer systems. First the high pressure, high temperature steam circuit used to generate electrical power and second the cooling circuit used to cool and condense the high pressure steam from the generator circuit. In additon there is waste heat available from the flue gases themselves and the cooling circuits for the carbon dioxide holding tank and the reaction tank. In the above station the condenser circuit is cooling 55 million litres per hour and the rise in temperature in this circuit is about 10 C. The heat available from the steam turbine circuit is therefore 2300 Gigajoules per hour. Taking the specific heat of the flue gas as approximating to that of air at 1000"C with the value of 1.192 Joules per gram per degree Centigrade, the 2102 tonnes of flue gas per hour at a temperature of 300 C are carrying 590 Gigajoules of heat. From the heat of reaction above the each gram moleucule of magnesium carbonate used produces 37.49 Kilocalories of heat and the rate of heat production is therefore 1200 Gigajoules per hour and thecompression of the carbon dioxide gas provides another 67 Gigajoules per hour.The total energy in these parts of the circuit is therefore 4157 Gigajoules per hour.

To obtain the sodium chloride for the the start up procedure of the operation of carbon dioxide removal requires the evaporation of 159 million litres of the sea water. Taking the value of the latent heat of evaporation of water as 2440 Joules per gram it requires 390,000 Gigajoules to evaporate such a volume with a temperature rise of 7 C.The heat carried by the steam cooling circuit is 2300 Gigajoules per hour and the evaporation of the above volume will take of the order of seven days to produce sufficient sodium chloride for one hour operation. Stock for this a seven day period at the replacement per hour rate of 1190 tonnes would comprise 250,000 tonnes of sodium chloride and would require about one year to obtain by the continuous evaporation of sea water.The above station will produce of the order of 16 million litres (3.5 million gallons) of pure water per day. The 250,000 tonnes of stock sodium chloride would have to be protected from the weather and the above weight of this compound has a volume of 110 million litres and a storage tank 60 metres in diameter and 40 metres high will be required to store the stock. Stock of dolomite for seven days is also required amounting to 200,000 tonnes with a volume 69 million litres requiring a storage tank 50 metres in diameter and 30 metres high.

The residual reaction solution is evaporated to recover the sodium chloride.

This can be performed either by adding it to the sea water evaporating system or prefferably by using available heat from and the flue gases and the compression and reaction tanks which totals 1857 Gigajouies per hour. The evaporation of the sodium chloride solution from one cycle will require 20 hours and therefore 20 separate evaporator tanks each holding one cycle of reaction solution are required for this process each 10 metres diameter 30 metres high. The solution would best be evaporated by first of all by preheating it with the heat from the cooling circuit in the gas holding and reaction tanks and then spraying it into a tank up which are passing the raw flue gases.The solubility of magnesium chloride in water is 360 grams per litre and the above weight of magnesium chloride will dissolve in 1.9 million litres and only 648 tonnes of sodium chloride will dissolve in the same volume. This will recover 3897 tonnes of solid sodium chloride from the reaction solution for each hour. Released during this process will be 60 million litres of carbon dioxide gas which pass on to the spray absortion tanks and 243 tonnes of magnesium carbonate which will react with and remove the acid gases from the flue gases. The solution is passed through filters during evaporation first to recover magnesium carbonate and then the sodium chloride, the magnesium chloride solution being disposed.

Construction Materials for the Tanks.

All forms of iron are attacked and corroded by the solutions involved in the above reactions. Iron is particularly prone to rusting when in contact with water containing carbon dioxide. Thus although steel has to used to provide the strength of the demand. The principal use of this compound is in the glass industry and the above rate of production would markedly reduce the price of this compound. Since there is an abundance of silica (sand) in the United Kingdom, which is the other principal compound used in the preparation of glass, the effect is likely to be that glass and glass products will decrease in price. Glass can be used in various forms and shapes, both non reinforced and reinforced. For example a bridge over the river Tay in Scotland has been constructed from reinforced glass fibre. Thus it is very likely that many of the uses of metals like steel and aluminium will in future be replaced by glass simply by a reduction in the cost of this material arising from the low cost and plentiful supply of sodium bicarbonate. Finally the above station will produce of the order of 16 million litres (3.5 million gallons) of pure water per day for supply to industrial and domestic consumers The excess of bicarbonate over world demand can be disposed of directly into the sea and since it is a component of the sea water it will not be environmentally damaging. The same is true of the magnesium chloride produced in the process.

Claims (3)

Claims

1. A process whereby the carbon dioxide gas produced by electrical power generating stations is captured and prevented from entering the normal atmosphere of the Earth.

2. A process whereby other noxious gases, such as sulphur dioxide and nitrogen oxides, are in addition prevented from entering the normal atmosphere of the Earth 2. A process whereby the products of the process in claims 1 and 2 can be safely disposed of into the oceans or onto the land without damage to the oceans or land part of the environment of the Earth.

3. A process whereby in achieving the aims in claims 1 and 2 produces useful industrial products of which purified calcium carbonate and sodium bicarbonate are examples.