Process for producing low-concentration gas mixtures, and apparatus for producing the same

A process for producing low-concentration gas mixtures, comprising the steps of:

• controlling the pressure of a raw gas;
• purifying the raw gas, thereby generating a high purity diluent gas;
• dividing said high purity diluent gas into first and second portions;
• controlling the flow rate of at least one high-concentration standard gas;
• mixing said first portion of said high-purity diluent gas and the high-concentration standard gas, thereby generating a medium-concentration gas mixture;
• dividing the medium-concentration gas mixture into a first flow and a second flow;
• mixing said first flow of said medium-concentration gas mixture with a second flow portion of the high-purity diluent gas, thereby generating a second medium-concentration gas mixture;
• dividing said second medium-concentration gas mixture into a first flow and a second flow;
• repeating (m) times the two above mentioned mixing and dividing steps to generate a first and a second flow of a (m)th medium-concentration gas mixture, with m varying from 2 to n-1;
• mixing the first flow of the (n-1)th flow of the (n-1)th flow of the medium-concentration gas with the nth flow portion of the high-purity diluent gas, thereby generating a low-concentration gas mixture;
• controlling both the pressure of said low-concentration gas mixture;
• and
• the pressure of the second flow of each of the first to (n-1)th medium-concentration gas mixtures downstream from their creation, the pressure of said second flow of the (m)th medium-concentration gas mixture (1<m<n-1) being smaller than that of the (m-1)the medium-concentration gas mixture.

An apparatus for producing low-concentration gas mixtures, comprising:

• gas line means;
• means for controlling the pressure (2) of a raw gas;
• means for purifying the raw gas (3), thereby generating a high-purity diluent gas;
• means for dividing (4) said high-purity diluent gas into a first and a second portion, said second portion flowing through first restricting means (R1);
• second restricting means (R3) through which said first portion flows;
• means for controlling the flow rate (7) of a high-concentration standard gas;
• means for mixing (50) the first portion of the high-purity diluent gas and the high-concentration standard gas, thereby generating a medium-concentration gas mixture;
• means for dividing (51) the medium-concentration gas mixture into a first flow and a second flow, said first flow passing through third restriction means (R2);
• means for diluting (52) the gas mixture of the first flow with said second portion of the high-purity diluent gas, thereby generating a low-concentration gas mixture;
• both means for controlling the pressure (14,15) of said second flow portion of the gas mixture, thereby controlling the pressure of said first portion and
• means for controlling the pressure (12,13) of said low-concentration gas mixture positioned downstream of the gas line means.

An apparatus for producing low-concentration gas mixtures comprising:

• gas line means;
• means for controlling the pressure (2) of a raw gas;
• means for purifying the raw gas (3), thereby generating a high-purity diluent gas;
• means for dividing (4) said high-purity diluent gas into n flow portions, each respective portion flowing through a respective first restricting means (R1, R3, R5, R7);
• means for controlling the flow rate (7) of a high-concentration standard gas;
• means for mixing (50) a first flow portion of the high-purity diluent gas with the high concentration standard gas, thereby generating a first medium-concentration gas mixture;
• means for dividing (51) the first medium-concentration gas mixture into a first flow and a second flow, said first flow passing through second restriction means (R2);
• means for mixing said first flow of the first medium-concentration gas mixture with a second flow portion of the high-purity diluent gas, thereby generating a second medium-concentration gas mixture;
• means for dividing said second medium-concentration gas mixture into a first flow and a second flow;
• means for mixing and means for dividing to generate a first flow and a second flow of a (n-1)th medium-concentration gas mixture;
• means for mixing (52) the first flow of the (n-1)th flow of the medium-concentration gas with the nth flow portion of the high-purity diluent gas, thereby generating a low-concentration gas mixture;
• both means for controlling the pressure (12, 13) of said low concentration gas mixture and
• means for controlling the pressure (14, 15, 23, 24, 33,34) of the second flow of each of the first to (n-1)th medium-concentration gas mixtures positioned downstream of the gas line means.