Process centrifugal compressors are the most critical rotating equipment installed in fertilizer plants. We mention for instance natural gas compressor, syngas compressor, refrigeration compressor and air compressor in ammonia plants, carbon dioxide compressor in urea plants and multi-service turbo-expander train in nitric acid plants.
Usually they are unspare machines, designed according to the international standard API 617.

Centrifugal compressorsProcess centrifugal compressors are really the heart of the plants, and like human hearts they need the best specialists to take care of them.

In the last decade, Casale has specified and supplied a remarkable quantity of new process centrifugal compressors, but also carried out the assessment of the performances and the revamping of several units.
Among Casale extensive list of experiences for these machines we can count:

  • New compressors and revamped compressors;
  • Single shaft compressors and integrally geared compressors;
  • Single casing, double casing and triple casing compressor train arrangements;
  • Steam turbine driven and motor driven compressors, fixed speed and variable speed;
  • Centrifugal compressors for synthesis gas, natural gas, ammonia, process air, nitrogen, tail gas, NOx gas, carbon dioxide;
  • Compressors from all leading manufacturing companies and from different countries like France, Germany, Italy, and Japan.
Axially split centrifugal compressor - Internals Axially split centrifugal compressor - Internals

In these projects Casale provided services of proposal evaluation, engineering, procurement, quality control, plant construction or construction management, commissioning, start-up and performance monitoring, depending on Customer request, involving all engineering disciplines:

  • Process (e.g. design of operating points, definition of utilities, P&IDs, control philosophy, anti-surge philosophy, HAZOP and SIL assessment);
  • Machinery (e.g. assessment of existing compressors, 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, testing at manufacturer workshop, site assistance, machinery diagnostic);
  • 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);
  • Civil & Structural (e.g. design of foundations and steel structures);
  • …and much more!

Integrally geared compressor - Internals Integrally geared compressor - Internals Integrally geared compressor - Impeller Integrally geared compressor - Impeller A successful project, which foresees the installation or the revamping of one or more centrifugal compressors, needs competencies at 360° in the field of engineering: nothing should be underestimated, and details are of the essence.
For one century Casale has designed new and revamped plants all over the world, so we can provide Customers with all our experience and passion concentrated in each single project.

  • Have your compressors reached the end of life after several years of operation?
  • Is your machine the bottleneck for plant production?
  • Do you want to increase performances?
  • Do you want to change the driver or the control system for energy saving?
  • Do you want to upgrade sealing system of your compressor, from oil seals to dry gas seals?

If the reply to one of these questions is ‘yes’ or even if you want to know how your compressors can be boosted and your plant modernized, then get in contact with Casale. Let us start the discussion about your compressors and we will see the economic benefit you could achieve.
With our values of innovation, excellence, quality, safety, ethics and environmental sustainability, Casale is ready to be the single partner for all your needs.

Case History


Replacement of the inner bundles of both casings of a syngas compressor, during the complete revamping of two ammonia plants under an EPC contract.


As part of the revamping project of two old ammonia plants for an important European Customer, Casale process department identified the necessity to modify the performances of the syngas compressors, leading to the need of revamping the machines. After having studied and discussed with the original equipment manufacturer (OEM) all the possible scenarios, it was taken the decision to keep existing compressor casings and to replace all the internals.

Revamping scheme Revamping scheme


  • Age of original equipment: at the time of revamping, compressors were more than 40 years old. That means that it was likely to have unexpected problems when disassembling the compressors and that the availability and reliability of engineering documentation was limited;
  • Time: the compressor revamping had to be performed during plant annual maintenance turnaround, in a short time frame and with precise and tight schedule, considering that the necessary bridge crane was needed also for the maintenance of the other machines installed in the same building, to be performed during the same shutdown;
  • No shop pre-assembly: since it was decided to replace the compressor internals only, keeping the existing outer barrel casings, it was not possible to pre-assemble the machines in vendor factory; inner casings and outer casings would have met at the first glance at the local site;
  • Split of work: during project execution, the customer decided to make some modifications to the compressor driver, contacting a local company. That was an additional interface to be considered, and high-level management capabilities were demanded to cope with the needs and requests of all parties.


New compressor internal bundle New compressor internal bundle New compressor outer “barrel” New compressor outer “barrel” As very first step, Casale organized a site survey and equipment site inspections with OEM during a pre-shutdown. The main scope was to check the actual conditions of the equipment and to ascertain that the tolerances and clearances shown on the original drawings were still applicable.
It absolutely had to be avoided to have interferences during the installation of the new inner casings inside the existing outer casings.
In fact, when one of the four casings was found to be out of specs, the purchase of new one was decided.

Then, in order to be sure to respect the schedule, each action was defined in advance considering all minimum details and all possible problems; a program of activities was issued on hourly basis for all the duration of the shutdown and kept updated constantly. Precise site procedures and instructions were issued and shared among all parties involved. A dedicated team of supervisors was assigned to these machines, and everything was kept under control until the restart of the plant.

Other interesting technical remark

During the engineering phase of the project, Casale proposed customer to change compressor shaft seals, based on old fashioned seal oil technology, in favor of the state-of-the-art dry gas seals.
The occasion was taken to investigate in detail the replacement of the existing shaft oil sealing system with new dry-gas sealing system, understanding the changes needed on the equipment and on the utilities consumption. Casale is therefore now able to share this knowledge with all customers who wants to upgrade the sealing systems of their compressors, eliminating the cost of continuous regeneration of the shaft seal oil and the content of oil in the process gas downstream the compressor.


The revamping of syngas compressor trains was successfully performed respecting the original time schedule. Performances and mechanical behavior (e.g. bearing temperature, shaft vibrations, etc.) met all the requirements.