Patent Application
20120151962
Ethylene is recovered from light gas mixtures such as cracked gas from hydrocarbon crackers which contain various concentrations of hydrogen, methane, ethane, ethylene, propane, propylene, and minor amounts of higher hydrocarbons, nitrogen, and other trace components. The recovery of ethylene from crude light hydrocarbon gas mixtures is an economically important but highly energy intensive process. A method of separating ethylene which is simple, durable and cost-effective is desirable
A method for the recovery of ethylene from an off-gas is provided. This method includes providing an ethylene containing feed gas stream, introducing the ethylene containing gas stream into a first cryogenic separation device, thereby producing a first condensed stream and a first ethylene poor stream, and introducing the ethylene poor stream into a first feed compressor, thereby producing a pressurized first ethylene poor stream. This is repeated three times, resulting in a pressurized third ethylene poor stream, which is introduced into a pressure swing adsorber, thereby producing a high purity hydrogen stream and a PSA tail gas stream. The PSA tail gas stream is into a PSA tail gas compressor, thereby producing a pressurized PSA tail gas stream, which is then combined with an ethylene containing gas stream to produce the ethylene containing feed gas stream. The first condensed stream, the second condensed stream and the third condensed stream are combined to produce a combined condensed stream, which is introduced into an ethylene separation column thereby producing an ethylene rich stream and a methane rich stream. The methane rich stream is introduced into a methane compressor thereby producing a methane fuel stream.
Illustrative embodiments of the invention are described below. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
As the off gas is chilled in the cold box, methane and ethylene condense and drop out as liquid stream. The stream is chilled in several stages to economize on the compression power of Feed Compressor.
The condensed stream is sent to an ethylene separator column, where ethylene is concentrated at the bottom and methane rich stream is removed at the top. The column is driven by providing heat in a reboiler from a suitable stream within the process. An ethylene rich stream may contain 50-99% ethylene, balance being mainly methane. This stream may be recycled to ethylene plant for further purification or further purified in a separate system.
Turning now to
The ethylene poor stream 107 is introduced into a pressure swing adsorber 109, thereby producing a high purity hydrogen stream 110 and a PSA tail gas stream 111. The PSA tail gas stream 111 is introduced into a PSA tail gas compressor 112, thereby producing a pressurized PSA tail gas stream 113, which is then combined with an ethylene containing gas stream 101 to produce the ethylene containing feed gas stream 102. The low pressure methane rich stream 114 is introduced into a methane compressor 115 thereby producing a methane fuel stream 116.
The ethylene containing gas stream 101 may have less than 10% ethylene. The ethylene containing gas stream 101 may have less than 5% ethylene. The ethylene containing gas stream 101 may have less than 60% methane. The ethylene containing gas stream 101 may have less than 50% hydrogen. The ethylene containing gas stream 101 may have a composition of about 40% hydrogen, about 58% methane, and about 2% ethylene. The high purity hydrogen stream 110 may have a pressure of about 300 psig. The methane fuel stream 116 may have a pressure of about 75 psig.
Turning now to
The second ethylene poor stream 210 is introduced into a second feed compressor 212, thereby producing a pressurized second ethylene poor stream 213. The pressurized second ethylene poor stream 213 is introduced into a third cryogenic separation device 214, thereby producing a third condensed stream 216 and a third ethylene poor stream 215. The third ethylene poor stream 215 is introduced into a third feed compressor 217, thereby producing a pressurized third ethylene poor stream 218. The pressurized third ethylene poor stream 218 is introduced into a pressure swing adsorber 219, thereby producing a high purity hydrogen stream 220 and a PSA tail gas stream 221.
The PSA tail gas stream 221 is introduced into a PSA tail gas compressor 222, thereby producing a pressurized PSA tail gas stream 223, which is then combined with an ethylene containing gas stream 201 to produce the ethylene containing feed gas stream 203. The first condensed stream 206, the second condensed stream 211 and the third condensed stream 216 are combined to produce a combined condensed stream 224. The combined condensed stream 224 is introduced into an ethylene separation column 225 thereby producing an ethylene rich stream 226 and a methane rich stream 227. The methane rich stream 227 is introduced into a methane compressor 228 thereby producing a methane fuel stream 229.
The ethylene containing gas stream 201 may have less than 10% ethylene. The ethylene containing gas stream 201 may have less than 5% ethylene. The ethylene containing gas stream 201 may have less than 60% methane. The ethylene containing gas stream 201 may have less than 50% hydrogen. The ethylene containing gas stream 201 may have a composition of about 40% hydrogen, about 58% methane, and about 2% ethylene. The high purity hydrogen stream 220 may have a pressure of about 300 psig. The methane fuel stream 229 may have a pressure of about 75 psig.
