Adsorbent storage of natural gas

.~pl~liEnergy, Vol. Printed

55, No. 2, pp. 71&U, :9X Published by Elsevier Science Lid in Great Britain. Ail rights reserved 0306.2619196$15.00-0.W

ELSEYiER

epzrtment

of Applied

Science, Brookhaven New

York

Yationat

E&oratory,

Upton,

11973. USA

Office of Alternative Fuels, US Department ashington, DC 20585, USA

of Energy,

The natural-gas vehicle represents a cost-competttive, lower-emission ~~ter~~t~ve to the gasoline-fueled vehicle. The immediate challenge that confronts the natural-gas vehicle is extension of its driving range. This paper addresses the question of driving range by reviewing the storage technologies for natural gas. Technical comparisons are made between storage systems for adsorbent, liquefied and compressed natural gas, ancF estimates are made of the costs associated with refuehng with compressed and adsorbent natural gas. We discuss ccl&on adsorbents, vehicle emissions, designs of storage tanks, cost and safety. For storage-tank system design, we advance the concept that carbon adsorbents, when used with conformable-shaped tanks offer a means of increasing onboard fuel storage and, thereby, the driving range of the vehicle. The cost envelope being assigned to this technology is US&2000 or Eess per vehicle for 10gallon gasoline-equivalent storage. For adsorbent ~at~~~~-g~s(ANG), this cost is based on 200 lbs of adsorbent at a purchase price of US$S lb-‘, a US&Y00 conformable tank and US$400 for miscellaneous hardware. ecause the volumetric storage density of ANG is similar to that of compressed naturalgas (CNG), the bene$t of the former is its lower operating pressure. Lower pressures have the advantages of small refueling costs, the availability of conformable tanks and safety, Our suggested soiution to the driving-range problem of a natural-gas vehicle is the use of improved adsorbents in a low pressure (500 psi) conformable-shaded storage tank. Published by Esevier Science Ltd

atural-gas

vehideS

research and engineeri gas passenger c e. This acceptant improve ambient systems for natural gas are necessary becaus the vehicle’s driving range to less than 2 compressed natural-g systems for vehicles. :ighted, with the a~~~rbe~t stor For passenger service, t riving-range and its fuel vehicles are fleet vehicle. The two typ private sectors. Pres resistance from Et is legislatively andated, but this growth is receivi operators because of the limited 200 mile driving ran . The three classes of storage ~ystem§

aul vehicles (i.e. trains, buses, trucks). eralPy support it as a. fuel been the storage system of choice, but For the passenger vehide, recent advances in approaching the stora levels of CiVG systems.

natural gas vehicle is that gas-injection teeb~~~~gy to starts. Although the

ee its emissions

h-pressure ( N 100 psi) acceleration and cold

Another classification in the types of NGVs of the storage tank; the two being consider formable.3 The obvious advantage of a conformab closer fit to the limited onboard storage space of a fuel tanks may be placed in the vehicle w~t~~~t sac cargo space. The disa vantage of a shaped tank is that pressure vessels require uniform internal stresses; a chain being only as

Aasorbent storage

as

itsweakest

ofnalwal

@Z,j

sses are a naerg~-aiconsequence IS!: ut a~~~ev~~~uniform stress Eeveis

1

ast several years, Brookha

g and room temperature,

the

volume of the tank. weight of the adsorbed temperature, carbon a

a vehicle’s storage syste is defined as the stored gas minus b ::oom temperature. 9x& total weight at

Comparison

sm-es less than 1 atm.

of ENG, CNG and ANG storage NG

Temperature

(“C)

(psi& Compressibility Stored density (kg liter-‘) Stored (v/v) Delivered (v/v) Fuel weight (kg) Fuel volume (liter) Tank shell vol. (liter) Einpty shell wt (kg) Carbon wt (kg) Total system wt (kg) T&al system vol. (liter)

25 0.1 14.7 1 0.00065 1 0

LNG

-170 0.35 50 0.42 636 57s 24.11 55.7 10 25 46.15 65.7

systems for 10 gal!on gasoline equivalent CNG lab

ANG

25 4.5 653 0.95 0.032

25 4.5 653 0.93 0.14 217 200 24.11 141.9 14.2 57.6 105 183.75 156.1

-

lab

CNG iab

CNG fastjiill

ANG

25 24.8 3600 0.86 0.18 277 257 24.11 93 6 78

2.5 24.8 3600

25 4.5 653

0.14 220 200 24.11 140,1 6 118

78 101

118 146

0.11 970 150 24.11 177.7 17.7 12 106.6 199.75 195.4

fast jill

Tkree carbons were

testes recerdy at

delivered methane gas; these carbons estvaco, and the Atlanta Gas and consortium of gas utiliti Amoco, Atlanta Gas a

mer. The activation pro The fact that d m, oxygen) treatment rent treatments all le seems to indicate the maximum st value. This premise also is supporte

e storage capacity carbo ity is close to the 200 v/v

The fuel density stored (pS) in a container that is at a temperature above the critical tern eratm-e is the sum of the a phase (p,) and gas phase (pg) densities, i.e. Ps = Pay; + Pg$ ivided by the ~o~tainer’§ volu ontainer’s volume.

sing the fact that

is the packing density, pC is the a is the weight ratio of adsorbate to a For methane, metric storage 61 re pp

sity

where 16 is the molecular weight of met of I mole of gas and (298/2?3) is a t~rn~~ratur~ ~~~r~etio~ factor.

pS = (0.17 - 0.032/2) x 0.5 + 0.032

-vs= 166.5 (stored) v

ressure of I a&n., roug

Presently,

Y

= 166.5 x 0.90 x 150 (deiiveredj

adsorbents

from coconut

shells, hard woo

Yess than 3000 psi as a actual volumetric storage

ie 1 lists the sizes and weights of a 5..I.4 million ga~~~i~e-e~uiva~e~t~ for the t e table shows the torage requires a cryogenic hen the vehicle is not bei re is nearly a 20% di

TU fuel tank (I 0 gal

actual refill. The former is e laboratory ~~easnred unt under e~~~l~br~~rnconditions, whille the latter is the amount el actually transferred in 5 min from .a 3600 psig refueling station. As ah-ea mentioned, this (20%) lsss in refueling is attributable to the hea compression, where, upon cooling, the gas settles to a pressure less 3000 psig. The concern is that a similar loss in refueling ca would occur for ANG storage fro the laboratory values. Thi in Table 1 by reducing NG storage from 22 to 170 for fast r-&h. A refueling losses have b n identified as pore lockage by impurities eats of adsorption. The goa s of adsorbent research are to: (1 cycling losses from gas impurities to less than 5% over 100 cy an adsorbent which can be regenerated with treatment; and (3) get an 80% refill in 5 min. In general, NGVs have a sohid safety record. The one area of ~on~e~~ is a sudden rupture of the tank either upon refueling or upon these cases, compressed-gas systems represent a potentia personnel and equipment because stored energy may be releas sudden isentropic depressurization. The major di compressed gas system and pressure. Compressed-gas syste erate at over six time s a factor of 10 less an adsorbent system, so that A energy than GNG, as given by the energy e~~at~~~ 200 scfm fueling

Misc.,Gross

*Capital

amortized

profit

station

@j Maintenance

over 5 years 50% utilization

atio of principal specific heats, which fm natur ction of stored gas energy ~ep~e~g~t~ a sign tage in the case of a ruptured tank. lower system pressure sf ANG also confers a U 5ecause of lower compressor costs an energy costs of camp e ~~t~o~ for the works required to press a gas is si ressed-gas energy stored equation

e flow rate, and N, the number of corn atio of the work between a two-stage g system, for the same capital and operatin ~a~~~lated9 by others; these costs are a breakdown of the the American Gas Association.

ajor disadvantage of an ~2200 lbs) factor. A&k shortens tbe vehicle’s ra

ment of Energy / Brookha

hese goals are for pipeline-gr

orous adsorbent

becau

kc; refuel were

her areas of con-

2. Wegrzyn, M. Give&h

7%

natural gas remain in the carbon bed on ~es~~~t~~~. constructed by placing an internal heater in a carbon b pounds (i.e. Cd an eater. As part of an automated cycle-testing facility which, in severa

NE yqram

Fig. 3. DBE/BNL

program

goal

onths, can simdate

for naiural-gas storage.

goal

for cost af adsorbent.

an a~~~rbe~t~~~orage

systemthat is

esides demonstrating the guard~~~~~gthe thermal distribution within t :o serve as a basis for devising a the Il. Finally, improvements in the st a arge part, due to improvements i re are in a large part; due to im ~d~orbe~t. Research is on-goin 1-l in the full-scafe veh US$5 lb-” or less to p tarting materials. This co while keeping the tot 00 per vehicle. igures 4 and 5 hst our program goals in develo c~~fo~rnab~e tanks. The improvement in space ut I 6, showing a pair of cylinders and a confor u!ar enclosure. The two cylinders occupy on1 le tank covers 75%. The goal for 1 e tank to utilize 80% of a r was set at US$7 1-r, or app nger car requires a minim ge. Recent designs from T fabricating tanks at one half this value; hence cost goal of the program. The costs of the USS3.35 I-” tank and the USS5 lb-”

Fig. 4. DOE/BNL

program

goal for on-board

space utilization.

b. WegrzyyM, M. Gurevich

Ieaves around ~J$~4~~ for the corn ment, while stiI1 meeting our over

natural-gag vehicles ane organic materials, a

57% space utilizatim -

Two cylindrical

guard of us

cl-

erectly have lower e

- -

75% space utilization

_.

tanks and a conformable tank within a system of rectangular section.

cross-

Aakwbent storage o~nat~ra~ gas

tlyless than those of gasoline e fact that NGVs have no ev ntegrity of the fuel tank and the fuel of these attributes were a xhe University of North 6, CO, aggregate toxi

tern is no%compromised.

emission rates were between 5 and 30 and 35 times lower, and the aggregat . Even NO, emission rates lower reactivity of total with those from i ustry-averaged gasoline (I n-like conditions in which as demonstrated for 7 shows the results when were held constant. Fig vehicle emissions were a from NGV emissions and e same amount of urban-like mixture at %hesame tota the same NO, in side-by-si g chamber. The UNC c haXves made of clear Te n atmospheres under near-out of s humidity. The test shown in pounds were adde test was 9: 1: at

0.50

.50

3.40

.4O

Fig. “I. Yoe-methane

emissions ozone-forming Carolina’s outdoor

potentia! from smog chamber.

the University

of North

me ~r~dmcti~n~ Howeve se testswere carried out ber e~v~~~nrne~~~ which not always reflect the va conditions of urban cities. ther studies with naturd gas tech ave been even ressive. The results for a California y, with emission rates fo wn Victoria, also are and NO, from one 0 .0001, 1.32 and 0.06 g mile-l, respectively.‘” and NO, emission rates from new-technolo because these are the prin a%precursor emissions for ozone fro icles. Lowering ambi ozone levels focuses on emissions and their reactivities in atmospheres with low and on reducing NO, in atmospheres with fore, from the standpoint of air pollution, es over ~onventio~a~~~ fueled gasoline vehicles.

Using carbon adsorbents in confo able tar&s gives natural-gas vehicles an alternative to compresse is God-pressure stora has the potential to increas risk factors and to reduce facing us are to increase th v/v by improving the ads times by controlling g . urities; and to ens by managing ther ging/discharging tests are needed to establish mum allowable working pressure of the co complete adsorbent/c vehicle to validate this te~hni~al/~ost approach

1. Ingessall, J. G., The

rgence of natural

gas as a trans

Physics Societyy, 1995,

Liss, W. E., Okazaki, S., Acker Jr, G. H. an . s., Fuel issuies for liquefied natural gas vehicles. U&-922360, 1992. 3. Konnodrornos, C., Fricker, N. and Sister, G., Development ~f~~~-~~~~n~r~~~~ tanks for Isw-pressure adsorbed natural-gas (ANG) storage in vehicles. IANGV Conference. 1994.

2.

Adsorbent storage ofnnaa.trai gas

4. Vdegrzyn, J., Weismann,

elspment Contractor

83

and Lee, T., Annual A ~oo~d~~atio~ Meeting (A

ologgi box!,

Porosity in Carbons Characterizations and A~p~~catio~~,ed. 5. W.

5.

lstead Press New York, 1994, Chapter 11. lith fabrication and microp bed natural-gas storage. G tive carbons for 9310240, 1993. 7 atranga, K. R., Myers, A. L. and Glandt, E. D., Storage of natural gas adsorption on activated carbon. Chemical Engiazeering Science, 1992,

6. Chaffee, A. L. et al.:

awicz, R. L., Bench mark your air coxnpressor, Plant Services, 1994,

derman,

R. J. and Blazek, C. F.

nomic anaIysis of low-pressure Technical highlights of E Paper 921551,

1992. ideout, G., Emissions testing of natural-gas/ga~o~~~e fueled vehicles. Joint Environment Canada-Canadian Gas Associat n Emissions Test Program3 Final report, Canadian Gas Associated, NGV evelo~~e~t Office, 1993.