Why not choose an optimal – proven – solution?

Are refineries spending more than they have to on inefficient heat exchangers just because they represent familiar technology? Nicholas Newman looks at why many refineries are looking to gasket-free, compact plate heat exchangers instead as a reliable, cost-efficient – optimal – alternative to shell-and-tube heat exchangers.

The most common heat exchanger in process plants today is the shell-and-tube. However, shell-and-tube heat exchangers are associated with high maintenance costs and excessive downtime. In addition, low thermal efficiency results in high installation costs and large footprints and excessive energy consumption and emissions.

Fully welded, gasket-free compact plate heat exchangers (CPHEs) from Alfa Laval, on the other hand, are a proven, cost-efficient alternative that offers advantages like:

• Reduced maintenance costs
• Improved reliability
• Better thermal efficiency
• Reduced heat-transfer area for lower CAPEX, energy savings and emissions.

Today Alfa Laval's CPHEs have been in long-term operation in critical processes in over 180 refineries worldwide.

The beauty of high turbulence and counter-current flow

CPHEs use corrugated plates between the heating and cooling media. This creates high turbulence and a cleaning effect that reduces chemical fouling.

CPHEs also have a multi-pass arrangement with an overall counter-current flow, which means more heat can be transferred from one stream to another, or a heating media can be used that is just a few degrees warmer than the cold media.

Together with high turbulence, this provides high heat recovery and high heat-transfer coefficients, allowing significant size and weight reductions, low acquisition costs (CAPEX) and reduced energy use and emissions.

Shear rate - a comparison

The maintenance requirements of CPHEs is based not on fluid velocities, as for shell-and-tube heat exchangers, but on the shear rate induced in the medias.

Normally, a shell-and-tube heat exchanger operating on crude oil, allowing a good velocity, would not even reach a shear rate of 15Pa. Under the same circumstances, but at a lower velocity and a higher friction factor, a CPHE achieves shear rates between 40 and 50 Pa.

The ratio between the two values gives a good idea of service duration before a shutdown for cleaning is necessary. The higher the shear rate, the longer the unit resists fouling.

Reliability and availability

Due to high turbulence and high shear rate, Alfa Laval's CPHEs have proven to provide many times longer uptime in critical refinery processes than shell-and-tube heat exchangers.

For example, one of the longest operating installations is in a bitumen refinery in Europe. Here, 14 CPHEs are in operation, the oldest since 1996. They have replaced shell-and-tube heat exchangers in duties such as ADU fraction cooling, VDU overhead vapour condensing and bitumen heating and cooling.

The shell-and-tube heat exchangers required cleaning and inspection yearly, which took a week. The CPHEs require only a day of chemical cleaning every third year. The refinery has reduced maintenance costs by 96%.

Mechanical cleaning

The advantage of chemical cleaning is of course that the panels of the CPHE do not have to be removed and as a result, maintenance time is reduced to a minimum.

However, if chemical cleaning is not sufficient, mechanical cleaning with a high-pressure water-jet is a relatively simple alternative. The panels can be removed, providing access to the complete plate pack, so there is no need to remove it.

In a European lube oil plant, for example, a CPHE has been in operation since 2004 as a condenser in the solvent recovery part of a paraffin removal plant. It needs cleaning every 12-15 months due to calcium-carbonate scaling. It is cleaned with high-pressure water of 800 - 1000 bars, using heated water and either rotating nozzles or nozzles with narrow spraying angles. The cleaning procedure, which includes opening, cleaning, closing and tight-testing, takes eight hours and can be carried out during one shift.

The CPHE replaced three carbon-steel shell-and-tube heat exchangers that had problems with corrosion. The same cleaning procedure for those heat exchangers took 2-3 days.

Reduced heat transfer area means lower acquisition costs

Because CPHEs are so efficient, they require relatively little heat-transfer surface compared to shell-and-tube heat exchangers.  This means one CPHE can often replace a number of shell-and-tube heat exchangers. So there are significant savings to be had in capital outlay. 

For example, in one planned installation, 12 CPHEs will replace 28 shell-and-tube heat exchangers for a savings of 36 million euro.

In addition the small size of CPHEs mean they require only a fraction of the space needed by shell-and-tube heat exchangers. So there are savings to be had on foundations, constructional steel work, and the like.

Finally lower energy use due to better heat-transfer efficiency and increased heat recovery gives reductions in operating costs and emissions. 

Global company, local insight

With a staff of over 100 specialists at offices in the United Arab Emirates, the Kingdom of Saudi Arabia, Iran, Egypt and Pakistan, Alfa Laval provides complete solutions for customers wherever they are, at every stage of their projects. Alfa Laval partners with its clients, evaluating their needs and processes and helping them design and implement the most reliable and cost-effective solutions possible.

In addition, Alfa Laval has service centres in the United Arab Emirates and the Kingdom of Saudi Arabia. This allows them to carry out field service, provide performance agreements, condition-based monitoring and maintenance across the Middle East.