Separation method and apparatus

A separation apparatus comprising:

• a compression system to compress a gaseous mixture thereby to produce a compressed stream and a purification unit connected to the compression system so that the compressed stream is purified;
• a main heat exchanger connected to the compression system having flow passages for subjecting the compressed stream to indirect heat exchange with mixture component streams;
• a separation unit having at least one distillation column to rectify the gaseous mixture contained in the compressed stream, thereby to produce the mixture component streams;
• the separation unit having a liquid outlet to discharge a liquid stream enriched in one mixture component of the gaseous mixture;
• the main heat exchanger connected to the separation unit such that the mixture component streams flow from cold to warm ends thereof;
• the main heat exchanger configured to discharge a first subsidiary stream and a second subsidiary stream at higher and lower temperatures, respectively, the first subsidiary stream and the second subsidiary stream made-up of the compressed stream;
• a turboexpander to expand at least part of a combined stream with the performance of work to supply refrigeration, the combined stream formed from a mixture of the first subsidiary stream and the second subsidiary stream and the turboexpander connected to the separation unit such that at least part of an exhaust stream of the turboexpander is introduced into the at least one distillation column;
• the compression system having a base load compressor, a turbine loaded booster compressor in flow communication with the base load compressor and operatively associated with the turboexpander to at least be partially driven by the work of the turboexpander and a further compressor connected to the turbine loaded booster compressor;
• the further compressor having inlet guide vanes or the compression system having a by-pass line having a cut-off valve to by-pass the further compressor when the cut-off valve is set in an open position such that the compressed stream is delivered from the further compressor or through the bypass to allow the pressure of the compressed air stream to be varied to in turn vary the refrigeration supplied by the turboexpander and production of the liquid stream such that increasing the pressure of the compressed stream in a high liquid mode of production increases the production of the liquid products and decreasing the pressure of the compressed stream in a low liquid mode of production decreases the production of the liquid products;
• a flow control network configured to mix the first subsidiary stream and the second subsidiary stream and thereby to form the combined stream, the flow control network having a first and a second pair of valves connected to the main heat exchanger to control flow rates of the first subsidiary stream and the second subsidiary stream, respectively, and therefore, the temperature of the combined stream to ensure that the exhaust stream from the turboexpander has an outlet temperature at least at about equal to saturation temperature and a static mixer interposed between the first and second pair of valves and the turboexpander to mix the first subsidiary stream and the second subsidiary stream;
• and
• each of the first and the second pair of valves containing a high flow control valve and a low flow control valve such that during the high liquid mode of production, the flow rates of the first subsidiary stream and the second subsidiary stream are able to be respectively controlled by the high flow control valve of the first pair of valves and the low flow control valve of the second pair of valves, the low flow control valve of the first pair of valves and the high flow control valve of the second pair of valves being set in closed positions and during the low liquid mode of production, the flow rates of the first subsidiary stream and the second subsidiary stream are respectively controlled by the low flow control valve of the first pair of valves and the high flow control valve of the second pair of valves, the high flow control valve of first pair of valves and the low flow control valve of the second pair of valves being set in closed positions.