Aluminum Brazed HEX Chart 015

8/11/2019 Aluminum Brazed HEX Chart 015

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Volume 10 Number 5 - May 2005


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A

s the need for increased supplies of natural gas

begins to intensify, so too does the battle to reducethe cost of processing the large natural gas reserves

in remote areas of the world. Many see liquefied natural gas

(LNG) as a significant player in this arena, as the design of

facilities and the equipment within them has made major

productivity and cost leaps in the last few years.

For decades, LNG plant designers were concerned first

and foremost with ensuring safety and reliability throughout

the processing cycle. And because facilities were so large in

size and scope, maintaining design uniformity from one

plant to the next remained standard practice.

Today, however, plant owners and operators face ever

increasing external costs that squeeze profitability.

Identifying efficient products and processes has conse-

quently become a critically important piece of the puzzle. As

technological innovation continues unabated, an industry

once reluctant to embrace change has opened its arms to it.

Consequently, the reduced cost of LNG per tonne for many

processors has been dramatic.

Most modern day engineers endeavour to lower costs in

three basic ways:

They explore and develop different processes by whichLNG can be produced.

They design larger plants using larger, more powerfulcompression equipment.

They integrate advanced heat exchanger and insulated

piping technologies into system designs.The refrigeration cycle requires a great deal of energy and

associated costs for LNG manufacturing. Given advances in

the technology and design of heat exchangers, plant owners

and operators are no longer limited to a one system fits all

approach. Additionally, products such as vacuum insulated

pipe (VIP) have gained a foothold in a growing number of

LNG processing facilities, thanks to their significant advan-

tage over traditional mechanically insulated pipe (MIP).

Therefore, there is no better time to evaluate the present

processing cycle and equipment, with an eye on its cost of

acquisition and daily operation; performance and efficiency;

processing capacity; quality and reliability; and impact on

environmental and energy efficiency requirements.Heat exchanger types and usesHeat exchanger technology in LNG plants ranges from shell

and tube to spiral wound, to a wide variety of compact heat

exchangers. In an effort to innovate and reduce cost of LNG

production, many LNG applications are now utilising com-

pact heat exchangers with highly effective heat transfer per-formance, resulting in reduced horsepower and increased

plant output vs. shell and tube or spiral wound exchangers.

Reprinted from HYDROCARBON ENGINEERING MAY 2005

Hot technology for

lower cost LNG

Dan Markussen, Chart Industries, USA, outlines how heat exchanger technologies and

vacuum-insulated pipe offer advantages that can lower the overall cost of producing LNG.

Figure 1. Competitive forces in the production ofLNG are forcing plant owner/operators to seekinnovative ways to lower costs.

Figure 2. The compact exchanger performance ofbrazed aluminum heat exchangers allowsowner/operators of LNG facilities to lower the costper tonne of LNG produced.

COVER

STORY


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Reprinted from HYDROCARBON ENGINEERING MAY 2005

Brazed aluminum heat exchangers (BAHXs) are highly

efficient, compact heat transfer devices offering advantages

over shell and tube. Produced by vacuum brazing, BAHXs

are used for a wide range of cryogenic and non-cryogenic

applications, including LNG and industrial gas production,

refinery and petrochemical processing, and hydrogen and

helium liquefaction. BAHXs are a well established technol-

ogy, and have been produced by Chart for 55 years.

BAHXs offer LNG processors the benefits of compact

design (typically 20% of the size of comparable perfor-

mance carbon or stainless steel shell and tube exchangers),

close temperature approaches (1 C/2 F), flow options, and

a unique ability to exchange heat with multiple streams (10

or more process streams are possible). Together, these

advantages can lower installation and operating costs, and

minimise engineering, insulation, support systems, testing,

documentation, transportation and site arrangements.

BAHXs also enable plant managers to reduce liquid inven-

tory and improve plant safety.

Related to BAHXs, Core-in-Kettle exchangers utilise a

brazed aluminum plate fin exchanger located within a large

cylindrical kettle. The aluminum plate fin exchanger

replaces the traditional tube bundle in a new or existing shell

and tube unit, typically one fifth of the weight of its shell andtube counterpart. The brazed aluminum construction also

eliminates mechanical joints and leakage potential.

Core-in-Kettle exchangers can reduce installation and

operating costs significantly. They use less insulation, and

require less liquid inventory and horsepower than shell and

tube exchangers. They can also improve the efficiency and

economy of chillers, vapourisers, reboilers and con-

densers. In fact, the design is so efficient that tight

approach temperatures down to 2 F (1 C) can be used,

thereby increasing plant capacity and reducing horsepower

requirements.

It is important to consider application limits for each of the

technologies described. BAHXs are limited to clean fluids typ-ical of hydrocarbon processing. Furthermore, fluids must not

be corrosive to aluminum. There are exceptions, however, for

trace amounts of mercury. Brazed aluminum equipment from

a recognised industry leader in technology innovation (such as

Chart Industries) is designed with mercury tolerance in mind.

Although mercury is highly corrosive to some alloys of alu-

minum, an optional proprietary mercury tolerant design can be

provided, allowing the exchanger to operate with mercury pre-

sent in the process fluid while the equipment resists corrosion.

To further take advantage of the increased performance

of compact heat exchangers, LNG plant designers are also

considering the use of compact welded plate heat exchang-

ers. Comprised of stacked, welded steel plates, and con-tained within the bounds of

bolted pressure plates,

welded plate heat

exchangers can be utilised

in services outside the tem-

perature limitations for

brazed aluminum exchang-

ers. The steel construction

of the welded plate

exchanger allows Chart

Industries to couple its

expertise in the cryogenic

processing industry withheat exchanger design,

and extend its competen-

cies to warm applications

and applications with large

Figure 3. Core-in-Kettles provide superior heattransfer performance for brazed aluminum heatexchangerS compared to traditional shell and tubeapplications.

Figure 5. Advancements in vacuum insulated pipe (VIP) technology have allowedproducers of LNG to take advantage of its lower construction costs and beneficialinsulating value.

Figure 4. Heat exchanger diagram.


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temperature differentials. LNG vapourisation is one applica-

tion that could utilise the novel approach of using compact

heat exchangers in LNG receiving terminals.

New piping technologiesThe transfer of LNG demands piping that is at once afford-

able and reliable. For decades, MIP stood as the industry

standard by which cryogenic liquids could be transferred for

multiple use. Recently, however, vacuum insulated pipe

(VIP) has emerged as a preferable alternative in many

areas, including LNG production, with clear advantages.

VIP was developed in the early 1950s as a means of

transferring fluids within a hydrogen liquefier system. Since

that time, it has been used by industrial gas producers/sup-

pliers, national laboratories, aerospace companies, the

National Aeronautic and Space Administration (NASA), food

processing operations, and the entertainment industry, to

transfer cryogenic fluids.

Laminar radiation shielded VIP is generally available in

rigid and flexible styles, with inner line diameters ranging

from 3/8 - 26 in. Its stainless steel construction, TIG welding,

mass spectrometer leak checking and extensive vacuum

retention testing helps to ensure reliable, maintenance free

service. This decreases the need for field welding, andresults in lower total cost and faster deployment.

The recent introduction of VIP for LNG transfer service

is a significant development for the industry. VIP has many

uses for LNG applications, including:

LNG tank riser. The long distance between the ground

and the top of a tank requires the strong support VIPprovides. This pipe within a pipe requires fewer sup-

ports, and the prefabrication makes installation fasterand easier.

Terminal ship jetty marker. High reliability and low main-tenance make VIP ideal for underwater applications

such as this.

Storage tank to vapouriser piping. VIP minimises bi-

phase flow, increasing useful product flow andvapouriser pump life.

Overall, VIP affords LNG plant owners and operators a

lower total cost than MIP. Consequently, system owners and

operators can avoid high installation labour costs, ongoing

maintenance, liquid losses and lost revenue due to longerdeployment times that are inherent in MIP installations.

Although VIP can represent slightly higher initial equipment

expenditure, significant savings are ultimately achieved

through reduced installation labour cost, minimal mainte-

nance, and less product loss over the life of the equipment.

ConclusionAs the drive to realise greater efficiencies and economies in the

LNG production process continues, technologies such as

brazed aluminum heat exchangers, Core-in-Kettle exchangers,

welded plate heat exchangers and vacuum insulated pipe, will

continue to grow in popularity. BAHXs clearly outperform their

shell-and-tube counterparts in areas of efficiency, innovation

and overall performance. Core-in-Kettle designs supplement

these benefits by offering added flexibility in replacing or retro-

fitting traditional shell and tube units. Welded plate heat

exchangers extend the benefits provided by BAHXs to applica-

tions outside of temperature limitations. Finally, VIP offers bet-

ter reliability and lower long term lifecycle costs than traditional

MIP. LNG operators that seek innovative ways to enhance prof-

itability and improve plant performance should consider lever-

aging these technologies to lower the cost per tonne of LNG

while expanding production capacity. _____________________

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Aluminum Brazed HEX Chart 015