4 PO 14 Sekiguchi

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Poster PO-14

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A SOPHISTICATED, LOW-COST, ENERGY-EFFICIENT,SMALL-CAPACITY LNG VAPORIZER AND ITS PRACTICAL USE

VAPORISATEUR DE LNG SOPHISTIQUE A FAIBLE CAPACITE

FONCTIONNANT A COUT REDUIT AVEC HAUT RENDEMENTENERGETIQUE ET SON APPLICATION PRATIQUE

Masaru SekiguchiTokyo Gas Co., Ltd.

Tokyo, Japanwww.tokyo-gas.co.jp/index_e.html

Hirokazu MoriTokyo Gas Engineering Co., Ltd.

Tokyo, Japan

ABSTRACT

Tokyo Gas in collaboration with Tokyo Gas Engineering has succeeded in developing

a completely new kind of compact LNG vaporizer for small-capacity LNG terminals. It

makes optimum use of ambient heat to vaporize LNG for the supply of town gas above

the minimum allowable temperature requirement, even in cold regions. The new

vaporizer costs 20% less to build than previous systems, and enables a massive 70%

reduction in operating costs through considerably reducing reliance on fuel as a heat

source.

LNG vaporizer systems in small-capacity LNG terminals have up to now had hot

water vaporizers for use during winter fitted alongside air fin vaporizers. The requirement

for additional equipment to provide a heat source for the hot water vaporizers also made

each system complex and costly. The new system combines an air fin vaporizer with a hot

air source in one unit. The resulting system is simple, can be used throughout the year

even in cold climates, and is very energy-efficient, and accordingly environment-friendly.

The very first unit was installed at the Tokyo Gas Kofu satellite terminal, where it

demonstrated excellent vaporizer performance. The first unit to be made commercially

available in the Japanese market was operated for over a year by Chubu Gas at its

Hamamatsu satellite terminal, and the units have been adopted for base load operation at a

large number of terminals, including some in cold regions.

RESUME

Tokyo Gas, en collaboration avec Tokyo Gas Engineering, a russi dvelopper un

vaporisateur de GNL compact de type compltement nouveau pour les terminaux de GNL

de faible capacit, ce qui permet lutilisation optimum de chaleur ambiante pour la

vaporisation de GNL en vue de la fourniture de gaz de ville une temprature infrieure

la valeur minimum admissible ou dans des rgions froides. Le cot de construction du

nouveau vaporisateur est infrieur de 20% celui des systmes prcdents, ce qui ralise

une forte rduction du cot dexploitation de 70% en rduisant considrablement ladpendance du combustible comme source de chaleur.

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Jusqu prsent, les systmes de vaporisateur de GNL des terminaux de GNL de faible

capacit utilisaient des vaporisateurs eau chaude pendant lhiver, en les installant juste

ct des vaporisateurs air ailettes. La ncessit dun quipement supplmentaire

destin fournir une source de chaleur pour les vaporisateurs eau chaude rend ainsi

chaque systme complexe et coteux. Le nouveau systme combine le vaporisateur air ailettes avec la source dair chaud dans un seul bloc. Le systme ainsi obtenu est simple,

capable dutilisation longueur danne et trs efficace sur le plan nergtique, do le

respect de lenvironnement.

Lappareil initial a t install au terminal satellite de Kofu de Tokyo Gas, o il a fait

preuve dexcellentes performances de vaporisation. Le premier appareil rendu

commercialement disponible sur le march japonais a t mis en service durant plus dun

an par Chubu Gas son terminal satellite de Hamamatsu, et les appareils ont t adopts

pour la demande de base dans un grand nombre de terminaux, y compris certains situs

dans les rgions froides.

1. INTRODUCTION

In areas of Japan where the supply of town gas through pipelines is not economically

feasible, LNG is transported by road tankers and other means from receiving terminals to

small-capacity LNG terminals, where the LNG is converted to town gas. There are

currently about 40 small-capacity LNG terminals in Japan, and more are expected to be

built in the future.

At small-capacity LNG terminals, the most common means of vaporizing LNG is to

use natural draft air fin vaporizers. These utilize ambient heat, and thus cost very little to

operate. However due to accumulation of frost on the heat exchange surface, the durationof continuous operation is limited, making changeover vaporizers essential. Moreover in

colder regions, hot water vaporizers and accompanying hot water generation equipment

are also needed to counter drops in the gas temperature at the exit from the air fin

vaporizer. As a result, the overall vaporizer system flow becomes very complex, making

for high construction costs, and the large amount of fuel required as a heat source for hot

water vaporizers in winter also makes operation very expensive.

To overcome these drawbacks, Tokyo Gas and Tokyo Gas Engineering developed a

new low-cost, energy-efficient vaporizer, known as an HAV (Hot air draft superheater

with Air fin Vaporizer), that incorporates a hot air source into a single unit based on a

conventional air fin vaporizer.

This report introduces HAVs, including the results of test operation of the first unit at

the Tokyo Gas Kofu satellite terminal, and also reports on the operating performance of

the first commercial unit at the Chubu Gas Hamamatsu satellite terminal.

2. CONVENTIONAL LNG VAPORIZERS SYSTEM

2.1. Natural Draft Air Fin Vaporizers

Air fin LNG vaporizers that made the atmosphere as the heat source are mainly being

used in Japan for small-capacity LNG terminals, where the amount of LNG handled isrelatively small.

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An example of the structure of an air fin LNG vaporizer is shown in Fig. 1. This

vaporizer has vertical heat exchanger tubes made from an aluminum alloy, with the fin

and the pipe being formed as a single unit by extrusion molding. The heat exchanger

tubes are connected to the header pipe or the bend pipe. The flow of an air fin LNG

vaporizer is shown in Fig. 2. The vaporizer consists of an evaporation part and asuperheating part. There are two types of natural draft air fin vaporizer. In one, the

evaporation part consists of parallel-connected heat exchanger tubes connected with the

header pipe, and the superheating part consists of serial heat exchanger tubes connected

with the bend pipe. In the other, both the evaporation part and the superheating part

consist of serial-connected heat exchanger tubes connected with the bend pipe.

A natural draft system is a system in which air convection occurs automatically from

top to bottom due to density change of the air cooled by the heat exchange with LNG.

This system is currently used in small-capacity LNG terminals because there is no need

for power to provide a heat source, but its continuous operation time is as short as about 4

hours. Moreover, when the air exchanges heat with the LNG, and its temperature drops,the moisture in the atmosphere condenses, producing clouds of mist, meaning that

consideration must be given to the surrounding environment.

Fig. 1 An example of the structure of an air fin LNG vaporizer

Fig. 2 The flow of an air fin LNG vaporizer

Plane view

Elevation view

Cross-section of a tube

Edge view

Heat exchanger tubeHeader pipe Bend pipe

Heat exchanger tube

Header pipeBend pipe

Vaporizer Superheater

Heat exchanger tube

Bend pipe

Vaporizer Superheater

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2.2. An Example of a System Configuration

The exit gas temperature of an air fin vaporizer does not exceed ambient air

temperature, and usually, because the moisture in the atmosphere freezes on the surface of

heat exchanger tubes and acts as heat resistance, exit gas temperature falls as operation

progresses.

Therefore, when exit gas temperature becomes lower than the minimum use

temperature of the piping material, the taking into account the relation between design air

temperature and design continuation operation time, either a hot water bath vaporizer is

installed alongside the air fin vaporizer, or an afterheater is installed downstream of the

air fin vaporizer.

Especially, in cold districts where the lowest temperature of a day becomes 0C or

less, either the hot water bath vaporizer is installed alongside an air fin vaporizer and used

in winter, or only the hot water bath vaporizer is installed and is used year-round.

The general example of a system configuration with a hot water bath vaporizer

installed alongside an air fin vaporizer is shown in Table 1. When supply capacity 1 t/h is

made into 100%, two air fin vaporizers of 100% capacity are installed, and it operates,

taking turns to stop for defrosting at regular intervals, in order to restrict the exit gas

temperature fall due to frosting on the heat exchanger tube surface. Moreover, the hot

water bath vaporizer of 100% capacity is installed for winter season operation. In order to

supply hot water to the hot water bath vaporizer, incidental facilities such as a hot water

boiler and a hot water pump are also installed.

Table 1 An example of system configuration

Supply capacity 1 t/h

Design pressure 0.97 MPa

Production gas

temperature

over 0C

Configuration Air fin vap.: 1 t/h x 2 units

Hot water vap.: 1 t/h x 1 unit

Hot water boiler: 400kW x 1 unit

Hot water pump: 7.5kW x 1 unit

Flow

Air fin

Air finLNG Gas

Hot water

Boiler

100%

Capacity:100%

100%

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3. HOT AIR DRAFT SUPERHEATER WITH AIR FIN VAPORIZER (HAV)

3.1 HAV Outline

A hot air draft superheater with air fin vaporizer (HAV) system was newly devised

and developed. The HAV system consists of a vaporizer, superheater, and hot air draftgenerator as shown in Fig. 3. After the forced-draft vaporizer makes maximum use of the

ambient atmospheric heat to vaporize the LNG (-162C in its liquid form), an auxiliary

hot air draft is produced in the superheater to boost the temperature of the gas.

3.2 Example of a Design for a New System

The changes during a day of the gas supply requirements determine the system

configuration of the HAV system. In a standard setup, two separate HAV setups are

installed, with each line having capacity equivalent to 50% of the maximum supply. Fig.4shows the pattern of operation with two lines operated according to the supply required.

An example of how a HAV standard system could be configured is shown in Table 2. The

elevation view and plane view of the HAV system is shown in Fig. 5.

It is basically possible to operate a single line continuously for 24 hours, and even

when weather conditions are severe (ambient temperature below 5C, snow or rain) it can

be run continuously for more than 13 hours. By installing two lines, gas can be produced

continuously according to the amount of supply required.

Fig. 4 Pattern of supply and operation

9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 1 2 3 4 5 6 7 8100%

75%

50%

Time

Supply

Line A

operation

Line B

operation

[Hot air draft generator]

Air AirCombustor

LNGNG

Su erheater

[Fan]

Va orizer

Fig. 3 HAV Outline

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Table 2 Example of configuration of a standard HAV system

Supply capacity 1 t/h


Production gas

temperature

over 0C

Configuration Vaporizer: 0.5 t/h x 2 units

Superheater: 600Nm3/h x 2 units

Hot air generator: 2 unitsFlow

Bypass piping (dotted line) connects the inlet piping

from each unit to the outlet piping of the other unit.

Fig. 5 Elevation view and plane view (1 t/h)

3.3 Features of the New Vaporizer System

(1) Low cost

Compared with systems that combine natural-draft air-fin vaporizers with hot water

vaporizers, the HAV is a simple system that makes the maximum use of ambient

atmospheric heat. Trial calculations were made for the installation of system with 1 t/h

supply capacity in a cold district. This achieves a 20% reduction in construction costs.

The design also produces a remarkable 70% reduction in operating costs, due to requiring

considerably less fuel as a heat source. Moreover, the installation space required for the

A line

B line

LNG Gas

Capacity:50%

50%

7 .4 m

5 .5 m 4 .0 m

A line

Vaporizer

Superheater

Hot air draft generator

Fan

5 .5 m

2 .8 m

B line

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vaporizer can be 25% smaller, and there is no need for space to install incidental facilities

such as hot water boilers.

(2) Use in cold regions

- Vaporizer: The fan located at the top of the vaporizer draws in large volumes of air,curbing the accumulation of frost and the resulting reduction in performance this

causes. The vaporizer also features newly redesigned air fin tubes with large

surface areas for heat exchange.

- Superheater: To ensure that the gas absorbs the heat of the hot air draft with

minimum waste, the gas and hot air flow in opposite directions, and tubes with a

large number of circular fins are used.

- Hot air draft generator: When the ambient temperature drops, the temperature of

the hot air draft can be raised to maintain the vaporized town gas above the

minimum allowable temperature requirements for the downstream piping material.

- Defrosting: Defrosting can normally be carried out by forced ventilation usingfans, doing away with the need for sprinkler-based defrosting systems. In

mid-winter, heat from the hot air draft can be used to augment normal defrosting

measures.

- Thanks to the above features, continuous operation where output matches town

gas demand is feasible without incidental facilities such as hot water boilers.

Moreover the HAV system can be used in cold regions where the ambient

temperature drops below 0C in winter.

(3) Calorific value stability of production gas

- Startup: When one line is stopped due to a change in gas demand during today,overheated gas from the operating line is connected to the stopped line. This setup

prevents calorific value fluctuation on starting because it purges LNG that remains

inside the vaporizer.

- Operation: The superheater structure is arranged so that flow is on the level or

descending in order to prevent fluctuation in calorific value due to retention of

fluid in the system and consequent evaporation of high calorific value components

if non-evaporated LNG enters the superheater.

(4) Mist prevention

- Problems with clouds of mist, arising in conventional air fin vaporizers fromcondensation of atmospheric water vapor, are resolved in the HAV by the fan on

top of the vaporizer, which disperses the water vapor before it can condense.

(5) High reliability

- The HAV uses aluminum alloy, well known for its excellent performance and

durability at low temperatures, as the heat exchange material.

- The fan and hot air draft generator are based on general-purpose products, the

durability of which has been proven by performance. We have also established a

speedy maintenance service.

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More than a year has now passed since installation, but the unit is still operating

reliably. The issue of clouds of mist produced when water vapor in the air condenses has

been resolved by fans installed at the top of the vaporizers to disperse the water vapor into

the atmosphere. The calorific value of the manufactured gas is extremely stable, and

operations such as starting up, shutting down, and changing the load are all easy toaccomplish.

Outline specification


Capacity 2.0 t/h

Vaporizer 1.0 t/h x 2 units

Superheater 2.0 t/h x 1 units

Hot air generator 1 unit

Fig. 7 HAV at Chubu Gas Hamamatsu satellite terminal

The operating data shown in Figure 8 is an example of energy-saving operation

implemented in December 2002, when air temperature was relatively low, but humidity

was relatively high. Apart from in mid-winter, the HAV system does not use fuel for

superheating. The vaporizer fans and the blower in the hot air draft generator are operated

instead, enabling the vaporizer to be operated in an energy-saving mode. The weather at

the time this data was recorded was rainy, (although the rain stopped in the early evening),

with an average air temperature of 6.3C, and a relative humidity of 80%. This shows

continuous operation for about 14 hours with an LNG flow of 2.0t/h. After operation, the

vaporizer outlet gas temperature had dropped to -9.7C, but the temperature of the

manufactured gas was 4.4C, with air from the blower keeping it above 0C by

superheating. This demonstrates that there is no need at all for fuel for the purposes of

superheating.

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Fig. 8 Data from a commercial unit in operation

6. CLOSING COMMENTS

LNG vaporizers are important components of satellite terminals. By making

maximum use of ambient heat, the newly developed HAV system achieves a considerable

reduction in energy consumption and a corresponding reduction in environmental impact

compared with conventional systems.

Features such as low cost, compactness, the non-generation of mist, and the ability to

function well in cold regions make the HAV an ideal LNG vaporizer for small-capacityLNG terminals.

Finally, the authors would like to record their thanks to the Chubu Gas and the staff of

its Hamamatsu satellite terminal for making available the precious operating data

resulting from the first use of the HAV system in Japan.

REFERENCES

1) Masaru Sekiguchi, Hirokazu Mori: Current Air Fin LNG Vaporizer, Piping

technology extra number, Sep. 2001, p.62-66.

2) Japan Gas Association: Recommended Practice for LNG Facilities in small

terminals, Aug. 2002, p.99-103.

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0

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8:00 12:00 16:00 20:00 0:00

Tim e

Temperature

Vaporizer exist gas tem p.

Am bient tem p.

Production gas tem p.

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4 PO 14 Sekiguchi