Installation and process for the preparation of hydrogen cyanide
Present invention relates to a process and an installation ( 100 ) for the preparation of hydrogen cyanide by the Andrussow process, and more precisely for improving the conditions of mixing the reactant gases before feeding the Andrussow type reactor ( 60 ), in order to improve safety, to avoid any risk of explosion and to produce HCN in safe and efficient manner. The installation is configured in such a manner that oxygen is pre-mixed with air with a ratio comprised between 20.95% and 32.5% by volume, preferably between 25% and 30.5% by volume; methane containing gas and ammonia are simultaneously added in the pre-mixture of oxygen-enriched air in such a manner that the volumic ratio of methane to ammonia is comprised between 1.35 and 1.02 depending on the content of oxygen into air; said obtained reactant gases mixture having a temperature comprised between 80° C. and 120° C., preferably between 95° C. and 115° C. for feeding the Andrussow type reactor ( 60 ).
1. An installation ( 100 ) for the preparation of hydrogen cyanide (HCN), said installation comprising:
A) an Andrussow reactor ( 60 ), in which is introduced a reactant gases mixture of methane-containing gas, ammonia and oxygen-enriched air, said mixture reacting inside said reactor ( 60 ) over a catalyst to produce HCN, and a first static mixer ( 30 ) designed to homogenize the composition of the reactant gases mixture before its introduction into the Andrussow reactor ( 60 );
B) upstream of said Andrussow reactor ( 60 ) according to the direction of gas flow, gas feeding pipes (P 1 to P 4 ) for feeding the installation with each reactant gas, a first unit (U 1 ) for pre-mixing oxygen with air before adding methane-containing gas and ammonia into the obtained pre-mixture of oxygen-enriched air, wherein said first unit (U 1 ) comprises flow rate controllers (D 1 ) for controlling the air flow, (D 2 ) for controlling the oxygen flow, and (D 3 ) for controlling the flow of the oxygen-enriched air, at least one oxygen online analyzer close to the flow rate controller (D 3 ), which regulates the flow of the oxygen-enriched air, and safety control valves (V 1 , V 2 and V 3 ), said first unit (U 1 ) controlling the ratio of oxygen to be added to the air and the composition of the oxygen-enriched air, said oxygen-enriched air comprising between 20.95% and 32.5% in volume of oxygen, and comprises a second static mixer ( 16 ) designed to homogenize the composition of oxygen-enriched air before the addition of methane-containing gas and ammonia;
C) a second unit (U 2 ), which is a premixing unit for premixing the methane-containing gas with ammonia that further comprises flow rate controllers (D 5 , D 6 , D 7 ), safety control valves (V 5 , V 6 , V 7 ), and a third static mixer ( 24 ) designed to homogenize the pre-mixture of methane containing gas and ammonia before its introduction into the oxygen enriched air stream, for adding simultaneously methane-containing gas and ammonia into the oxygen-enriched air, with a volume ratio of methane to ammonia, being between 1.02 and 1.35 depending on the proportion of oxygen into the oxygen-enriched air;
D) at least one heat exchanger ( 13 , 15 , 21 , 23 ) placed respectively on each gas feeding pipe (P 1 to P 4 ) of the installation ( 100 ) for heating each gas stream separately, before its pre-mixing with another gas, in order to have a temperature of said reactant gases mixture feeding said Andrussow reactor ( 60 ) between 80° C. and 120° C.;
E) one filtration device ( 10 , 14 , 20 , 22 ) placed respectively on each gas feeding pipe (P 1 to P 4 ) of the installation ( 100 ), and one filtration device ( 31 ) placed on a feeding pipe (P 7 ) of the Andrussow reactor ( 60 );
F) a washing device ( 12 ) designed to wash the air before its premixing with oxygen when the temperature of said air is lower than 70° C., said washing being made with water, having a temperature between 15° C. and 30° C.;
G) a steam injection device ( 12 ) designed to inject steam into the air before its pre-mixing with oxygen; and
H) a control unit ( 50 ) connected to an alarm and that controls the ratios of (O 2 +air)/(CH 4 ) and of (O 2 +air)/(Ammonia) and able to manage a regulation of the flow rate of each reactant gas around a predetermined set value, said control unit being connected to said flow rate controllers (D 1 , D 2 , D 3 , D 5 , D 6 , D 7 ), placed on each gas stream, and to said safety control valves (V 1 , V 2 , V 3 , V 5 , V 6 and V 7 ), that are closed in case of a discrepancy between a set value and measurements made by said flow rate controllers (D 1 , D 2 , D 3 , D 5 , D 6 , D 7 ).
2. The installation according to claim 1 , wherein said Andrussow reactor ( 60 ), said first static mixer ( 30 ), said second static mixer ( 16 ), said third static mixer ( 24 ), said heat exchangers ( 13 , 15 , 21 , 23 ) said gas feeding pipes (P 1 to P 4 ), and said washing device ( 12 ) are made of stainless steel.