AlfaRex as cargo condenser

　

■Introduction

Up till now shell and tube heat exchangers have been used for as gas condensers on board all LPG ships. One reason for this is in the past no gasket free plate heat exchangers that can use for seawater as cooling media have been available.

PHEs with gaskets can normally withstand up to 3Mpa in test pressure and they have limitations regarding temperature. Special plate exchangers like the laser welded and totally gasket free AlfaRex can withstand up to 4Mpa.g design pressure and temperature from -10℃ to 350℃.

　

■Shell & Tube vs. PHE

All LPG ships have until now used S&T type cargo condensers, but due to corrosion problems S&T heat exchangers sometimes need to be re-tubed or replaced. Because of their heavy and large size, this is a cost and time consuming that normally has to be done at a shipyard.

PHEs have benefits as followings.

PHE benefits

- Small physical dimensions (See the table figure 1)

- Installation for existing vessel is easy (minor pipe work needed)

- No corrosion: e.g.a PHE can last the lifetime of the ship

- High efficient heat exchanges reduce burdens on the cargo compressor; specially when existing S&T condensers are replaced with PHEs.

　

■Features

1)　Durability

In the AlfaRex, the plate pack is laser welded in only two dimensions, in the planes of the plates (x.y.). This allows the entire plate pack to expand and contract freely along the length of the plate pack as temperature and pressure fluctuates.

AlfaRex has unique and simple design that's totally gasket free. It handles temperature from -10℃ and +350℃ and pressure up to 4Mpa.g.

The AlfaRex has passes grueling fatigue tests at the Alfa Laval process Laboratory.

The AlfaRex endured the full schedule of 20,000 temperature cycles with no indication of fatigue failure.

In each cycle, temperature fluctuated between 10℃ and 95℃ with a temperature gradient of 5-6℃ per second throughout the test.

　

　

2)　Spaces With thinner plates and highly efficient heat exchanges, AlfaRex could weigh 80% lighter and occupy 90% less space.

　

COMPACT ADVANTAGES

1)　A close temperature approach (small temperature difference between media) allows more efficient energy recovery.

2)　A lower hold-up volume allows more precise process control and improves safety when working with hazardous media.

　

Fig. AlfaRex compared with shell & tubu

　

Alfa Laval K.K.

Address: Nissin Bldg., 8-27, Kohnan 1-chome, Minato-ku, Tokyo 108-0075

Tel: +81-3-5462-2446　Fax: +81-3-5462-2455

URL: http://www.alfalaval.co.jp

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