Light olefins, defined herein as ethylene and propylene, serve as feeds for the production of numerous chemicals. Olefins traditionally are produced by petroleum cracking. Because of the limited supply and/or the high cost of petroleum sources, the cost of producing olefins from petroleum sources has increased steadily.
Alternative feedstocks for the production of light olefins include oxygenates. In an oxygenate to olefin (OTO) reaction system, a feedstock containing an oxygenate is vaporized and introduced into a reactor. Exemplary oxygenates include alcohols such as methanol and ethanol, dimethyl ether, methyl ethyl ether, methyl formate, and dimethyl carbonate. In a methanol to olefin (MTO) reaction system, which is a type of OTO reaction system, the oxygenate-containing feedstock includes methanol. In the reactor, the methanol contacts a catalyst, preferably a molecular sieve catalyst, under conditions effective to create an product effluent comprising desirable light olefins.
The product effluent from an MTO reaction system is then directed to a separation system including one or more separation devices, which are well known in the art. The separation system separates the desirable light olefins from other components in the product effluent such as unreacted feed and undesirable byproducts. MTO separation systems typically include one or more compressor units or bodies, which are adapted to compress at least a portion of the product effluent. The compressors have the dual purpose of facilitating the movement of the product effluent through the separation system as well as condensing out heavier less-desirable components from the product effluent.
Compressors such as centrifugal compressors are often formed of a body having one or more stages. Each stage has a respective inlet and outlet and usually includes one or more sections, each having an impeller and a diaphragm. In many instances, multiple bodies and stages are used. To reduce the power required to drive these multiple stages, intercoolers are often placed between them. An intercooler is a heat exchanger situated immediately downstream from a compressor. In some cases, intercoolers are also used between stages to reduce the power required for compression.
Compressor fouling may occur in compressors or intercoolers found in an MTO separation system. Fouling is the build up of a solid, e.g., crystal, or a layer of liquid hydrocarbon contaminants within a compressor or intercooler. For example, the liquid contaminants may form through polymerization within the compressor body. Compressor fouling in an MTO separation system is undesirable because as contaminants build up inside the compressor, imbalances may develop causing vibrations, compressor inefficiency and, ultimately, compressor failure. Contaminants also may solidify or condense in the compressor intercoolers. Fouling in compressor intercoolers is undesirable because heat transfer is impaired and flow rate is reduced.
It is therefore desirable to have a process for removing contaminants that have accumulated on the internal surfaces of compressors and intercoolers in an MTO separation system.