6 May 2020

At the LLC SIBUR Tobolsk site, the reconstruction and technical re-equipment of the propylene recovery unit (PRU) have been completed. The working medium here is off-gas – a mixture of propylene and nitrogen.

PRU returns to the production cycle more than 95% of propylene and about 80% of nitrogen, which remain in the off-gas after the main production. In the course of operation, the URP provides itself with process nitrogen from the off flow, thereby achieving savings in its consumption.



The unit is based on gas compressor and membrane technologies; its main elements are GEA Grasso screw compressors (of 1st and 2nd compression stages), a Silica drying module and a Borsig membrane subassembly. The maximum capacity of PRU is 1,340 Nm3 / h.

At the preliminary phase of the project, an audit of the input and output gas pipelines, a technical audit of the compressor, process and electrical equipment of the PRU were conducted.

Based on the results of the inspection, the scope of the work to be done was determined, defect sheets were drawn up, recommendations were prepared for replacing faulty and worn out assemblies and elements. A plan for carrying out local restoration works, major repair and upgrade of the unit, as well as a schedule of pre-start activities which include adjustment, its own and integrated testing of the PRU, were drawn up.



At second project stage, the feeding pipeline was upgraded. It is now equipped with highly efficient filtration system from ENERGAS. The degree of gas purification is 99,9% for particles larger than 1 microns and droplet liquid. The throughput of the filtration system is identical to the capacity of the PRU.

The system of two filters of vertical cartridge type is made on an open frame (with roof from rainfall) and according to the process flow scheme of gas treatment is installed before a first compressor stage. Filters for two-stage purification are equipped with pressure differential sensors that signal the contamination of filter elements and, accordingly, increase the degree of protection of the compressors. Control system for equipment is integrated into ACS of propylene recovery unit.



The three stage consisted in the implementation of a scope of works to upgrade and bring the unit to modern standards for the production and operation of gas compressor equipment:

1. A new screw oil-filled compressor of 1st stage is installed.

2. Obsolete capacity control system is replaced. The ability to stabilize the gas pressure at the inlet to the first stage compressor was added, eliminating pressure drop resulting due to a decrease in the volume of incoming off-gas. Taken together, these updates allow the PRU to correctly respond to changes in load under various operating modes of a main production.

3. Maintenance of oil systems of both stages of the unit were performed. At the 1st stage, the oil system was also cleaned from contaminants formed during the destruction of the compressor. All filters have been replaced. Refinement and filling of the necessary types of oils into each of the stages of the PRU was completed in accordance with the operating conditions and the component composition of the gas.

4. Complete maintenance (according to regulation 8000) of the compressor module and drying module was carried out.

5. The inlet line was purified from propylene dust and oil that got into the gas pipeline by reverse flow during the periods of emergency shutdowns of the equipment.

6. The unit’s software was updated, additional safety algorithms were included for trouble-free operation.

7. There were added set points and protections. PRU was pressure testing with nitrogen – checking all assemblies and connections for tightness.



At the final phase (after start-up and adjustment works and own tests) there was took place integrated testing of equipment under load in the general cycle of the propylene production plant. Gas filtration system and recovery unit have operated in normal mode, without any complaints.

The project on restoration of the scheme for rational utilization of off-gas was performed by leading engineers of the ServicENERGAS LLC (part of ENERGAS Group) together with specialists of companies SIBUR Tobolsk, Enerproject SA and Borsig MT. As a result, along with efficiency, environmental friendliness of production has also been increased, since until the unit was launched, all the off-gas was flared.



REFERENCE:

At the Tobolsk industrial site of PJSC SIBUR Holding the production of monomers (formerly Tobolsk-Neftekhim) and polymers (formerly Tobolsk-polymer), the capacities of the Tobolsk CHPP and the largest petrochemical complex in Russia ZapSibNeftekhim, was integrated into a single cluster.

SIBUR Tobolsk is a hydrocarbon processing enterprise. The productive capacities of the company include: a central gas fractionation unit for processing a broad fraction of light hydrocarbons with a capacity of 8 million tons per year; production of monomers for the production of liquefied hydrocarbon gases, butadiene, isobutylene, and methyl tert-butyl ether; production of polymers for the fabrication of polypropylene with a capacity of 500 thousand tons per year; power generation with a capacity of 665 MW for electricity and 2,585 MW for heat.

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