Sulzer Pumpen explains how retrofitting trumps the repair/replace dichotomy

Pump operators are often confronted with challenges, such as the decreasing reliability or efficiency of their equipment. These operational challenges can be caused by wear over time or by changed operating conditions, e.g. variations in well pressure in oil production or an increasing need for flexibility in power generation.

In such a situation, operators must either repair or retrofit their equipment. Repairs restore the original pump and remedy only the symptoms of the problem. By contrast, retrofits are able to eliminate the root causes of the problem, thereby sustainably improving the reliability and efficiency of existing pumps in operation. Retrofit solutions enable pump operators to keep pace with continuously changing requirements. The mean times between repairs and the operational life of pumps can be drastically increased, with attractive payback periods ensuring a quick return on investment.

Changing conditions are a huge challenge for pump operators. Not only can operating costs skyrocket, but the risk of production downtime can too

Sulzer can perform retrofits on virtually any pump, regardless of its age or original equipment manufacturer. With its global competence and service centre network, Sulzer provides retrofit solutions and 24/7 support for customers worldwide. Sulzer’s broad expertise – which includes advanced simulation capabilities on mechanical integrity and hydraulic design, expertise in materials and coatings, and excellent proficiency in reverse engineering – is the basis for successful and sustainable retrofit solutions, to the benefit of pump operators worldwide.

Case in point
Changing conditions are a huge challenge for pump operators. Not only can operating costs skyrocket, but the risk of production downtime can too, which is unacceptable, especially in critical businesses like oil and gas, power, and water. The example of a water injection pump retrofit shows how Sulzer can help to ensure reliable operation and reduce energy consumption.

A major oil company runs an offshore platform on the Norwegian continental shelf in the North Sea. On this platform, two Sulzer HPcp BB5 pumps have been in operation since 2002. They reinject water produced by the platform into the well to increase the pressure in the oil field and enhance oil production. These pumps were designed for a flow of 331 cubic metres per hour and a head of 1,558 metres. One of the pumps served as a standby unit in case of failure, while the other was in operation. In the years following the installation, it became apparent that the well required less than two-thirds of the originally specified discharge pressure. That meant the pump needed to be throttled, and a lot of energy was lost. In 2009, the situation deteriorated further because the process conditions changed once again. At that point, the required pump flow doubled, while the required pump head further decreased. A single pump could not achieve the higher capacity by itself. However, operating both pumps in parallel was also not an option; without a standby unit, a failure would lead to a considerable production loss. That risk was not one the company was prepared to take.

The operator asked Sulzer to evaluate the possibility of rerating these pumps to provide more flow so the injection requirements could be met with only one pump. During these discussions, the desired duty flow for each pump was set at 660 cubic metres per hour (or as close as possible) at a discharge pressure of approximately 100 barg (pump head 840 metres, suction pressure 10 barg).

Tailored retrofit
Sulzer conducted a hydraulic study at one of its global retrofit competence centres in the UK. The company’s engineers determined the optimal hydraulic design for the confines of the existing barrel casing, while reusing as many of the existing cartridge components as possible. The components retained from the existing design included mechanical seals, bearings, and coupling assemblies, as well as the electric motor.

Sulzer had several hydraulic designs that were geometrically similar to the one required for this application, but they were too large to fit this injection pump barrel. However, by adopting the proven laws of dynamic similitude, Sulzer physically scaled down the designs so the operating conditions were satisfied. This approach had the advantage of allowing the engineers to reliably predict the new, scaled performance from experience. The effects of incremental changes to this basis are well understood, and allow the base performance curve to be modified to suit individual applications. To accommodate the flow increase, Sulzer had to increase the impeller outlet passage width, which also required an increase of the distance between each stage. Sulzer replaced the following components: all impellers, all series stage diffusers, the last-stage diffuser, the pump shaft, and the balance drum and liner.

Because of the higher velocities in the pump suction nozzle caused by the increase in duty flow, the pump required a new advanced suction inlet casing design. Sulzer conducted a full computational fluid dynamics analysis on this new design to ensure an ideal distribution of flow was achieved from the inlet to the suction impeller eye. To verify the integrity of the pump mechanics, Sulzer performed a full rotor dynamic analysis at the retrofit centre.

Energy savings
Performance testing confirmed the retrofitted pump met the new duty conditions (in compliance with the API 610 technical standard). The retrofit was completed using a reasonable number of the existing cartridge components and without modifying the existing motor. The new cartridges were installed in the existing barrel casings after only one week per cartridge. None of the piping or major site ancillary equipment needed modification. Since the retrofit, the customer has been able to achieve the required water injection performance with one pump alone. One pump is therefore left as a standby unit, and the risk of injection failure – and consequent production loss – is minimised.

The duty flow required to achieve 100 percent operation with one pump was achieved with a significant reduction in pump discharge pressure, meaning surplus pressure no longer has to be throttled down across valves, saving a significant amount of energy. To achieve 660 cubic metres per hour with the two existing pumps operating together, 3,804 kW of absorbed power at the pump coupling would be required. The retrofitted cartridge requires only 1,875 kW to achieve the same flow in singular operation. The energy saving of 1,929 kW in input power amounts to more than 16.8m kWh annually. At an energy unit cost of $0.06 per kWh, the recurring savings translate into more than $1m per year. Thus, the payback period of this retrofit was less than one year. After a Sulzer retrofit, pumps are performance tested at one of Sulzer’s test beds to ensure optimum operation.