Hydraulic Power Recovery Turbine

Hydraulic turbines allow to convert the liquid inside CO₂ absorber of an ammonia plant into mechanical power.
This is just one of the various revamping activities that a chemical plant can undergo to achieve higher energy saving.

A typical situation where action can be taken to achieve this occurs whenever a high pressure fluid has to be throttled to meet the downstream process steps. Pressure reducing valves are generally used to dissipate, and thus waste, this hydraulic energy.

Figure 1 - Power recovery scheme Going into the specifics of ammonia production plants, this happens in the CO₂ removal section of an ammonia plant. The key equipment of this section is the CO₂ absorber, a tall column used to remove the CO₂ from the feed gas. This column is filled with a carbon dioxide absorbing solvent that flows down the absorber while the feed gas flows up. The pressure head of the liquid inside the column can be converted to mechanical power through a hydraulic turbine instead of being dissipated.
In addition to economic benefits, the installation of a hydraulic turbine also includes environmental benefits, mainly due to the reduction of emissions (carbon dioxide, carbon monoxide, etc.) that is achieved when the same energy would be otherwise generated through the combustion of fossil fuels.

Casale has developed a power recovery scheme focused on energy saving projects (see figure 1). Basically, this power recovery system consists of a modified API 610 heavy duty centrifugal pump working in reverse flow, so that it can operate as a centripetal turbine (hydraulic power recovery turbine, HPRT). The power recovered by this turbine is typically used to drive the semi lean pumps in the CO₂ removal section. These pumps are usually driven by an electric motor, so a significant amount of energy can be recovered by coupling the HPRT to the existing pump train. The recovered power is typically around 400 kW for a 1750 STD ammonia plant, this allows a significant reduction of the electrical consumption.

Figure 2 - HPRT train

Figure 2 shows the HPRT train described in the 1^st case history: the new items supplied by Casale are highlighted in green, the existing items are highlighted in blue. One-way mechanical clutch is used to allow starting of the other items before the HPRT is brought on stream.

HPRT

HPRT HPRT Over the last years, Casale has optimized the workflow and can fully support the Customers for this revamping activity.

The first step is usually a site survey to gather data and check dimensions of the existing machines. This is crucial to assure that the existing items can be fitted on the new baseplate.

As a next step, Casale carries out the technical evaluation of potential suppliers and takes care of the follow-up after the purchase order, including the quality inspections during the manufacturing.

The performance test is often critical for the HPRT since this type of machine usually requires a fine tuning to achieve the theoretical recovered power.
For this reason, Casale always requires the performance test for the HPRT, this will assure the End User to obtain the predicted recovered power.

The final step is the installation of the new items at site, Casale supervisees these activities, including the grouting of the baseplate and the alignment of the complete train.

Case History 1

Context

1750 STD Ammonia plant revamping for energy saving.

Scope of work

One hydraulic power recovery turbine has been installed on an existing steam turbine-driven pump train in an ammonia plant, the new turbine will be operated by the pressure head available at the CO₂ absorber.

Constraints

Installation activities to be performed during plant shutdown;
Existing pumps and steam turbine to be reused and fitted on new baseplate;
New couplings for the existing pumps and steam turbine;
New mechanical seal flushing system for the hydraulic turbine;
State-of-the-art over-speed and monitoring systems to be implemented.

Solution

Installation of a new hydraulic turbine along with a mechanical clutch, to be fitted on a new baseplate along with the existing pumps and steam turbine, taking in charge all the activities, from procurement to testing and commissioning at site.

Result

New and existing machine successfully tailored to Customer’s requirements.

Case History 2

Context

1050 MTD Ammonia plant revamping.

Scope of work

To take advantage of the pressure head available at the CO₂ absorber, one new hydraulic recovery turbine has been coupled to the existing electric motor-driven pump train installed in an ammonia plant.

Constraints

Installation activities to be performed during plant shutdown;
Existing pump to be reused and fitted on new baseplate;
New mechanical seal flushing system for the hydraulic turbine;
State-of-the-art over-speed and monitoring systems to be implemented.

Solution

Installation of a new hydraulic turbine, mechanical clutch, gearbox and electric motor to be fitted on a new baseplate along with the existing pump, taking in charge all the activities, from procurement to testing and commissioning at site.