A poor turbine back pressure and loss of efficiency has implications with regards to equipment operation. That real world impact differs depending on what service the equipment is in. The financial impact will be directly linked to the site’s steam generation costs and the value of the power or process that the turbine is driving.

These turbines are working to driving compressors, pumps, or blowers. Turbines in this service are normally used to support other processes within a facility. Most of these systems are critical and plant operation depends on them. When a turbine exhaust condenser is operating at a poorer pressure the turbine efficiency suffers and the turbine needs more steam to produce the same amount of work. In this type of service, the requirements of the process often dictate how much work has to be done by the turbine.

These turbines are working in conjunction with a generator to produce power. When a turbine is doing less work in this service, it means that the turbine generator produces less power for the same amount of steam usage. In order to compensate, more steam is needed to maintain the same MW output. The additional steam will have a direct cost to produce or if more steam can’t be generated the reduction in MW output will reduce how much power can be sold to the grid or used by the facility.

A reduction in turbine back pressure will also limit how much power can be produced at the upper end of the turbine’s operating range. There is a point where more steam cannot be produced or additional steam cannot physically be put through the turbine. This can be particularly important for peaking plants or when validating a system’s maximum capacity and power output, as some facilities have a financial incentive to maintaining a certain amount of power generation capacity.

Inadequate Air Removal – It’s understood that air may leak into the condenser from various connections. While the condenser sets the operating pressure, the air removal equipment needs to remove air from the condenser at the vacuum that condenser wants to operate at. If the air removal system is unable to do this, the condenser pressure will degrade. If the system has excessive air leaks or if the air removal system is mechanically damaged or has inadequate utilities, then it will cause a poor turbine back pressure. Issues with air removal often lead to large and dramatic losses of vacuum.

Cooling Water Problems – The cooling water temperature and flow have a direct impact on condenser performance. Any loss of cooling water flow or increase in the cooling water supply temperature will have a negative impact on the condenser LMTD calculation and will result in a poorer operating pressure. Over time it’s not unusual for additional heat load to be placed on the cooling tower and an increase in the flow rate demand from additional processes. This along with fluctuations in seasonal temperatures can lead to reduced condenser performance.

Fouling – The steam side of a turbine exhaust condenser is normally clean, assuming that the site does not have issues with steam quality. If there is a steam quality problem normally the turbine is also impacted with turbine blade erosion, silica build-up, or other issues. The majority of the condenser fouling in this service comes from the cooling water side of these units. Poor cooling water treatment can result in large deposits inside of the condenser tubes. Debris from the cooling tower can also cause problems. If the condenser is fed with river water, sediment debris may be a concern. Annual tube cleaning is important to maintaining performance.

This concludes our discussion on turbine back pressure. If you have any questions about your condenser performance or issues with your turbine back pressure, please don’t hesitate to contact Graham Corporation for assistance. Graham has engineers who specialize in helping ensure that equipment is operating to its full potential, and Graham personnel are available by phone or in person at site to assist with any required troubleshooting.