Title of Invention

"A PROCESS FOR SEPARATION OF SULPHUR TRIOXIDE FROM A GASEOUS MIXTURE"

Abstract

"A process for separation of Sulphur trioxide from a gaseous mixture containing sulphur dioxide and sulphur trioxide". This invention relates to a process for separation of Sulphur trioxide from a gaseous mixture containing sulphur dioxide and sulphur trioxide having an advantageous application in the sulphitation of cane juice which comprises in the steps of burning sulphur in a furnance at a temperature of 300°C, in the presence of oxygen to produce a gaseous mixture or stream containing sulphur di oxide and sulphur trioxide, subjecting such a gaseous mixture to the steps of cooling, first step of cooling is carried at a temperature of 130-145°C, introducing cooled gas mixture into an absorber column as herein described, the temperature of absorber column is 130-140°C, for absorbing sulphur trioxide, said absorbent comprising a sulphur and amine based compound as herein described and ethoxylate as surfactant subjecting the mixture to second stage cooling at a temperature of 60-70°C.

Full Text

FIELD OF INVENTION This invention relates to a process for separation of sulphur frioxidc from a gaseous mixture containing sulphur dioxide and sulphur trioxide By way of example, the process of the present invention can advantageously be employed in the step of sulphitation for producing sugar from sugarcane juice. BACKGROUND OF INVENTION In the process of producing sugar from sugar cane mixed juice, it is generally known in the art to heat mixed juice in a heat exchanger, and then introduce the heated juice into a sulphitor for removal of non sugars Fror this purpose, a gaseous mixture comprising sulphur dioxide and sulphur trioxide is introduced into the sulphitor so as to react with the mixed juice to form a precipitate containing non sugars and leaving sugar in the sulphited juice. Lime is added to the mixed juice in the sulphitor prior to addition of sulphur dioxide and sulphur trioxide so as to adjust the pH of the juice and allow the formation of calcium sulphite in the precipitate Calcium sulphite present in the precipitate also entraps the impurities, namely non sugars. The presence of sulphur trioxide constitutes a distinct and acknowledged disadvantage in such a process. Sulphur trioxide reacts with calcium to produce calcium sulphite, which is substantially soluble and goes into solution with sugar, and consequentially lowers the yield of sugar. Though the presence of sulphur trioxide is a recognized disadvantage, such a disadvantage was accepted in the art, as the step of sulphitation with sulphur dioxide was important for removal of the non sugars. Hitherto, the sulphur dioxide was produced by burning sulphur in a furnace in the presence of oxygen. Besides sulphur dioxide, sulphur trioxide is also formed as excess oxygen is always added to drive the reaction forward. The gaseous mixture formed from such a reaction can contain as much as 5 to 25% of sulphur trioxide based on the weight of sulphur dioxide, the amount of sulphur trioxide being dependant on the controls, such as of temperature, moisture and amount of excess oxygen employed in the process of burning sulphur. The gaseous stream exits from the furnace at a temperature of approximately 300°C and is passed through first and second stage coolers so as to reduce the temperature to approximately 70°C. It has been found that substantial corrosion occurs in the second stage cooler or heat exchanger. Yet another disadvantage is the presence of calcium sulphite present in the sulphited juice which causes down stream problems as scales deposit on the system, and thereby affects the heat transfer. A further disadvantage is that sulphur trioxide with moisture forms sulphuric acid, which results in corrosion and also reduces sugar. OBJECTS OF THE INVENTION An object of this invention is to propose a process for removal of sulphur trioxide from a gaseous mixture containing sulphur dioxide and sulphur trioxide. Another object of this invention is to propose a process for removal of sulphur trioxide from a gaseous stream containing sulphur dioxide and sulphur trioxide, which can advantageously be employed in the sugar industry. Still another object of this invention is to propose a process for removal of sulphur trioxide from a gaseous stream which avoids downstream corrosion in a sugar mill. Yet another object of this invention is to propose a process for removal of sulphur trioxide from a gaseous stream which is efficient. Further objects and advantages of this invention will be more apparent from the ensuing description. BRIEF DESCRIPTION OF THIS INVENTION According to this invention there is provided a process for separation of Sulphur trioxide from a gaseous mixture containing sulphur dioxide and sulphur trioxide having an advantageous application in the sulphitation of cane juice which comprises in the steps of: i) burning sulphur in a furnance at a temperature of 300°C, in the presence of oxygen to produce a gaseous mixture or stream containing sulphur di oxide and sulphur trioxide, ii) subjecting such a gaseous mixture to the steps of cooling, first step of cooling is carried at a temperature of 130-145°C, introducing cooled gas mixture into an absorber column as herein described, the temperature of absorber column is 130-140°C, for absorbing sulphur trioxide, said absorbent comprising a sulphur and amine based compound as herein described and ethoxylate as surfactant subjecting the mixture to second stage cooling at a temperature of 60-7QOC. In accordance with this invention, the gaseous mixture containing sulphur trioxide and sulphur dioxide from the furnace is passed through a first stage cooling and in a manner known as such in the art. The outlet temperature of the gaseous mixture from the first stage cooling is approximately 130-140°C, and preferably 135°C. In accordance with one embodiment of this invention, the cooled gas mixture is treated with an absorbent after the first stage cooling, treated in an absorber column and then subjected to a second stage at a temperature of 60-70°C. The temperature in the absorber is 130-145°C. In accordance with another embodiment of this invention, the gas mixture from the first stage cooling is subjected to a second stage cooling and the cooled gas is then treated with an absorbent. The step of treatment with an absorbent causes a removal of sulphur trioxide and the treated gas mixture containing sulphur di oxide is then introduced into the sulphiter. It will be apparent that the disadvantage associated with the process of the prior art are now obviated and the yield of sugar increases, as the sulphiting gaseous mixture now introduced into the sulphiter no longer contains sulphur trioxide. Preferably, the temperature of the absorbent, when introduced into the absorber, should be at room temperature. The reaction between the absorbent and gaseous mixture is exothemic in nature, and accordingly the temperature of the absorbent. The period of the reaction is dependant on the flow rate of the absorbent. The absorbent comprises:- i) Sulphur compound 11-17% ii) amine compound 1-6% iii) water 35-70% iv) surfactant, such as ethoxylate 0.3 to 2% The sulphur and/or amine based compound are absorbents, water is carrier and remover of heat generated during the reaction and can also constitute an absorbent. The volume of absorbent should be 10 to 201 for every 1000 to 5000 litres of gaseous mixture. The absorbent may be recycled/reused. Further objects and advantages of this invention will be more apparent from the following example:-EXAMPLE INLET TO ABSORBER SO2, % v/v 8.1 SO3, %v/v 1.1 TOTAL, % v/v 92 AIR BALANCE Flow rate 50 l/min into absorber I STAGE COOLING Outlet Temperature 132°C II STAGE COOLING Outlet Temperature 60°C ABSORPTION Flow rate of Gaseous Mixture 50 l/min Inlet Temperature 60°C Total volume of gaseous mixture 3000 L Volume of Absorbent 15 L per 1000-5000 L SO3 after passing through Absorbent NIL Outlet Temperature 62 ABSORBENT CHARACTERISTICS Sulphur Compound (as S) : 11-17% Amine : 1-6% Surfactant (ethoxylate) : 0.3-2% Water : 35-70% CLAIM; 1. A process for separation of Sulphur trioxide from a gaseous mixture containing sulphur dioxide and sulphur trioxide having an advantageous application in the sulphitation of cane juice which comprises in the steps of : i) burning sulphur in a furnance at a temperature of 300°C, in the presence of oxygen to produce a gaseous mixture or stream containing sulphur di oxide and sulphur trioxide, ii) subjecting such a gaseous mixture to the steps of cooling, first step of cooling is carried at a temperature of 130-145°C, introducing cooled gas mixture into an absorber column as herein described, the temperature of absorber column is 130-140°C, for absorbing sulphur trioxide, said absorbent comprising a sulphur and amine based compound as herein described and ethoxylate as surfactant subjecting the mixture to second stage cooling at a temperature of 60-70°C. 2. A process as claimed in claim 1 wherein the gaseous mixture containing sulphur trioxide and sulphur dioxide from the furnace is passed through a first stage at an outlet temperature of preferably 135°C. 3. A process as claimed in claim 1 wherein: i) Sulphur compound 11-17% ii) amine compound 1-6% iii) water 35-70% iv) surfactant, such as ethoxylate 0.3 to 2% 4. A process for separation of Sulphur trioxide from a gaseous mixture containing sulphur dioxide and sulphur trioxide substantially as herein described and illustrated.

Documents:

781-del-2001-abstract.pdf

781-del-2001-claims.pdf

781-del-2001-correspondence-others.pdf

781-del-2001-correspondence-po.pdf

781-del-2001-description (complete).pdf

781-del-2001-form-1.pdf

781-del-2001-form-18.pdf

781-del-2001-form-2.pdf

781-del-2001-form-3.pdf

781-del-2001-form-4.pdf

781-del-2001-form-5.pdf

781-del-2001-gpa.pdf