Valves supplier Bilfinger Intervalve Africa (BIA), in conjunction with engineering, construction and maintenance services provider Steinmüller Africa, both of which are subsidiaries of Bilfinger Power Africa, is investigating the steam systems of a paper mill to allow for possible improvements to be made. BIA will provide the valve expertise and knowledge and Steinmüller Africa, owing to its vast knowledge of the power industry, the required engineering.

BIA was approached by a major paper mill in KwaZulu-Natal to investigate the rapid deterioration of the plug and seat rings in the mill’s desuperheater spray water valves and started the investigation last month, says BIA technical sales consultant Peter Underhill.

“As the investigation ensued, it was determined that the valves were not operating in a desirable control range, which could be the system, and not valve-related,” he explains.

BIA and Steinmüller Africa’s approach is to fully understand the process and ensure that all the process conditions to which the spray water valves and desuperheaters were subjected, were logged.

“Once this is complete, we will recommend any equipment changes to avoid spray water trim deterioration and, by careful optimisation of the desuperheater nozzle and spray water trim size and style, possibly improve overall desuperheating performance,” Underhill tells Engineering News.

Meanwhile, he comments that top performers in the paper and pulp industry are constantly striving to increase productivity and quality while minimising costs. The main aspects that need to be addressed in achieving operational excellence are a reduction in energy costs, chemical use, production downtime and process variability.

“The correct selection, monitoring and servicing of control valves can result in financial rewards for clients,” he points out.

Underhill mentions that the functions of control valves in the paper and pulp industry are extremely diverse. They range from the required accuracy of the dosing valves and the tight control and fast-acting requirements of the basis weight valve, to the severe service requirements of the power and steam system such as the control of cavitation and noise.

Careful consideration should be given to the selection of a control valve, as the specific function which it needs to fulfil in sizing and style has to be considered, he states.

Underhill explains that the process of selecting the correct size, style and characteristics of a valve is paramount in the initial stages of a project. Incorrect sizing of the control valve could result in the valve not operating in a good control range, leading to the possibility of excessive wear and loss of controllability.

Certain valves have been specifically designed to operate in different applications – incorrect selection can lead to cavitation or flashing damage, excessive plant noise and poor control in areas such as basis weight, affecting paper quality. Valves used in incorrect applications can lead to undesirable process variability.

Control valve assembly consists of three prime components – the valve body, actuator and positioning. These components need to work in harmony with one another to fulfil the client’s control requirements. Poor performance of any of these components can lead to poor control of the process, leading to unacceptable process variability that can seriously affect the user’s bottom line, he explains.

The advent of smart positioners on control valves, as well as emergency shutdown valves, has resulted in many benefits for the client, Underhill notes. The Fisher DVC2000 and DVC6200 series digital valve controllers add accuracy of the valve position to allow tighter adherence to the required process setpoint, along with valve diagnostic capabilities that will determine the health of the valve.

Using the downloaded information from the device, either from advanced diagnostics or the online performance diagnostics, allows for maintenance programmes to be adjusted to cater for the more problematic valves. This will avoid the removal and stripping of valves that are in good health, which is costly and time consuming, he explains.

Overlaying downloads obtained from valves over time will assist the client in moving to predictive maintenance and reducing expensive stockholding of spares.