FEATURE PUMPS, VALVES & ACTUATORS FLUSH OUT PLANT INEFFICIENCIES


Richard Smith, at AESSEAL, looks at how appropriate selection of mechanical sealing systems for pumps can have an impact on the energy efficiency of a plant


n Europe and the United Kingdom, it is estimated that around 10% of electrical power is used for pumping equipment1


I ,


which is a significant part of running a manufacturing operation. One of the consequences of this is that regulatory bodies in the UK, as well as plant owners themselves, are focussing on improving the energy efficiency of pumps and pumping systems. Mechanical seals can have an influence on the energy efficiency of a process. Their purpose is to seal the process fluid - whether it is toxic or expensive, the objective is to keep it within the system and pipework to avoid it seeping out and resulting in a cost for lost process fluid and clean up. And, of course, if the liquid or process fluid that is leaking is heated, it is losing costly energy from the system. So, be it with flanges, valve stems or pump seals, it is necessary to think of the seal not only as preventing process fluid contamination and leakage to external atmosphere, but as an important part of conserving energy within the system. Mechanical seals on pumps are probably


the most delicate components and we use seal flush plans to change the environment that the seals operate in, to help them provide reliable operation. So, in simple terms, flush plans are used to create a stable and idealised environment for the seal, and are formalised by the American Petroleum Institute in their standard API-682, the custodian of the flush plans, where they are detailed in standardised formats.


API PLAN API Plan 21 DESCRIPTION Cooled by-pass flush A survey was carried out by the Fluid


Sealing Association (FSA) for pumps incorporating a total of 28,000 seals where the process temperature exceeded 200°C. Figure 2 shows the most popular flush plans used and, by comparison, the energy absorption of each. It is interesting to note that flush plan 32, the second most commonly specified in the survey, is by far the highest energy user. Looking at studies on different flush


plans undertaken by the FSA, we compare some single seal flush plans (21, 23, 32 and 62) with a hypothetical case study. The configuration is a hot oil pumping application with single stage, end suction centrifugal pump (API 610 compliant), based on: Pumped fluid: hydrocarbon at 315°C Specific gravity: 0.8 Specific heat: 1.67 kJ-°C (0.4 BTU/lb-°C) System pressure: 345 kPag (50psig) in


seal chamber Pump driver: 50 HP (typical) Sealing devices: Compression packing,


mechanical seals Assumptions: Heat lost at the pump


must be replaced at the system boiler / heat exchanger [see API Plan table at bottom of page].


Figure 2 (above): The most popular flush plans and their energy usage


To put these figures into context, if a OBSERVATION


A hot process continually cooled by-pass flush means poor energy efficiency


API Plan 23


Cooled closed-loop flush More efficient closed-loop circuit that dissipates heat generated at seal faces only


API Plan 32 Cool external flush


Constant cold clean external flush directly into process fluid is very energy inefficient. Heat required to compensate for injection of cool flush.


API Plan 62


Dead ended / steam quench Very efficient – uses little steam and has no effect on process temperature


18 MAY 2017 | PROCESS & CONTROL


SEALING SYSTEM POWER CONSUMPTION 37.8kW/hr


1.7kW/hr


pump is running 24 hours a day, 365 days a year the difference between flushing a seal using API Plan 32 and API Plan 23 can see a business save around 400,000 kW of energy a year. When this saving, which equates to a 96% reduction in energy costs, is spread across multiple pumps and multiple locations the potential savings are huge. Selection of inappropriate sealing systems can have a significant impact on the thermal efficiency of a plant and plant utilities. Sealing systems found in industrial applications, even when functioning as intended, can be wasteful of energy. However, there is raising awareness of the technology that can overcome some of this wastage. Being able to choose between different


47.4kW/hr


sealing systems or flush plans requires a good understanding of the principals of their operation and why they’re used. The best way to access this knowledge is to work with a sealing partner that has the understanding of this specialist area.


0.8kW/hr* (If well maintained, if not 1.8kW)


1 https://www.youtube.com/watch?v=FvPRTowCK-E


Aesseal www.aesseal.com


/ PROCESS&CONTROL


Figure 1: API Plan 62 - this method is efficient, uses little steam and has no effect on process temperature


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