Special purpose steam turbines

Special purpose steam turbines are commonly used in fertilizer plants as drivers for critical compression services, for instance the critical syngas train, and are normally designed according to API612.

Special purpose steam turbine

Casale has specified and supplied a remarkable quantity of new steam turbines for new plants and has assessed plenty of existing steam turbines in case of plant revamping.

Casale has proven experience as an international world-class Process Licensor and EPC Contractor, for the realization of new LSTK projects and for the revamping of existing plants. Casale machinery engineers have experience, competences and background, not only to cope with the execution of the mentioned projects but in general to cope with any kind of technical challenge related to selection, testing, installation and operation of machinery installed in fertilizer plants, including the special purpose steam turbines.

As EPC Contractor Casale is able to supply new steam turbines from recognized Vendors, being in charge for their engineering, procurement and quality control, up to and including shipping, erection and commissioning at site, depending on Customer.
As Process Licensor, Casale is able to optimize the steam consumption of each steam turbine in harmony with the overall steam balance of the plant, and at same time control the CAPEX costs. In case of revamping of existing plants, where commonly old turbine and compressors are installed, Casale project team will assess the performances of each machine, with focus on the possible impacts of their aging effect on the overall process performances. As outcome of this assessment, Casale can identify which machine can be re-used and which ones need to be modified to fit with the new revamped capacity and efficiency, with the best CAPEX/OPEX balance.

More specifically either for new plants or revamping projects Casale can become the focal point for the Customer, handling all the activities of different technical disciplines:

• Process (e.g. steam balance, utilities, P&IDs, control philosophy, HAZOP and SIL assessment etc head);
• Machinery (e.g. assessment of existing turbines, issue of all technical specifications necessary for inquiry and purchase, selection of preferred supplier, review of technical documentation, technical coordination of all the other involved disciplines, site assistance);
• Piping & Layout (e.g. revision of plot plan, new pipe routing, line modelling, stress analysis);
• Instrumentation (e.g. specification of new control valve and recycle valve, integration of new system with existing DCS and ESD, definition of minimum requirements for critical and special instruments with membranes);
• Civil & Structural (e.g. design of foundations and steel structures);
• …and much more!

Casale is therefore able to re-design the plant with the guarantee of the perfect balance among investment cost, service life and process flexibility.

The scope of engineering services covered by Casale can be tailored on Customer requests, involving also local construction contractors.

Case History 1

Context

Turbine replacement for existing compression train, ammonia revamping project.

Backgroud

As part of the revamping project of a big ammonia plant for an important American Customer, Casale process department identified the necessity to significantly modify the steam balance of an old turbine (driver of refrigerant train) and to add a controlled extraction. This necessity was confirmed by the overall assessment made by Casale on the CAPEX/OPEX aspects of the revamping, therefore Casale decided to substitute the turbine with new one to be installed on the existing foundation. Moreover, the implementation of a new turbine was highly beneficial from efficiency perspective low steam consumption.

Constraints

• Space: the new machine required installation on existing foundations and coupling to existing compressors. Moreover, the position of the existing condenser was near the existing turbine, significantly reducing the available space for the new turbine with additional controlled extraction (refer to the below pictures).
• Time: the turbine replacement had to be performed during plant shutdown, in a short time frame of 4 weeks.
• Engineering: important efforts have been spent to integrate the new machine in the existing train. Casale followed all the below aspects and more:
  • The foundation was modified;
  • A new oil system was assessed and installed;
  • The existing control system was modified to accommodate the control and the instrumentation of the new turbine, including the additional controlled extraction;
  • All mechanical interfaces with the existing train were studied and all necessary verification of the train axis were performed.

Solution

Complete replacemente of the steam turbine with a new one with higher efficiency and with additional controlled extraction.

Result

Steam Turbine replacement successfully achieved according to the schedule without any major issue. Smooth operation with satisfactory performances in line with expectations and process needs from the very first start-up.

3D model showing the new steam turbine which fitted perfectly with the existing space constraints

Case History 2

Context

Turbine complete overhaling and adaptation to new process conditions of a new plant.

Backgroud

As part of the duties included in a LSTK project for a new Urea production plant, Casale was requested to re-use an existing CO₂ compression train having a special steam turbine as a driver, which was originally intended to be used for the revamping of another Urea plant present in the complex, but which was never installed and left stored for many years in Russia.
Casale was therefore in charge either of the verification of the original design with respect to the new plant needs, and of the verification of the mechanical integrity, since the equipment was kept stored outdoor for several years in Russia.

Constraints

• Location: it was not possible to move the equipment out of Russia or to a service center recognized by the Original Vendor.
• Time: all necessary inspection and overhauling activities needed to fit with the construction schedule.
• Certification: the existing equipment was certified according to GOST standards before the issue of the more recent EAC/TR CU regulations.

Solution

• Casale identified and qualified two local shops in the plant area, where inspection and overhauling were carried out including:
  • Rotor balancing verification, including rotor bowing assessment;
  • Campaign of NDT tests of critical parts (e.g bearing pads);
  • Functional tests on critical devices (e.g. governor valves);
  • Inspection and calibration of all instruments and control components (e.g. Bently Nevada components).

• Casale performed a complete re-engineering of the turbine and of the package to fit with the design of the new plant, including:
  • Implementation of turbine control logic in the new DCS of the new plant;
  • Performances verification with new steam balance with original OEM, identification of modification materials required (e.g., new extraction valve to fit with bigger extracted flow).

Result

Engineering activities were completed, the turbine was successfully inspected and overhauled. It is currently installed on its foundation on site and remaining erection activities are in progress according to the schedule.

Steam turbine rotor on low speed balancing machine, local shop