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17HBS9,ВОДОРОДНАЯ ЭНЕРГЕТИКА И ТРАНСПОРТ
Хранение водорода HYDROGEN ENERGY AND TRANSPORT
ч Hydrogen storage
LOW-TEMPERATURE REGENERATION f
OF CRYOSORPTION DEVICES IN HEAT-INSULATION CAVITIES 1 OF HYDROGENOUS CRYOGENIC TANKS i
и
ь
A.L.Gusev ы
с a
Scientific Technical Centre "TATA" ^
P.B.O. 787, Sarov, Nizhny Novgorod region, 607183, Russia §
Tel.: +7 (83130) 97472; Tel./Fax: +7 (83130) 63107; E-mail: gusev@hydrogen.ru ®
As a result of hydrogen leaks into heat-insulating cavities through microcracks as well as at the expense of gas release from the walls, a situation may arise related to untimely supersaturation of cryosorption pumps (CSP) with hydrogen [1, 2]. As it is known, the complete regeneration of ceolyte CaEH-4B requires the temperature of 473 K. It is impossible to reach this temperature without terminating the technological storage process for built-in CSPs. To reduce a negative effect related with this situation the possibility of low-temperature built-in cryosorption device regeneration was investigated on the base of the CaEH-4B adsorbent in a heat-insulating cavity of a hydrogenous cryogenic tank with substituting feeding. Using the Henry equation for the interval 20.2-32 K the desorption dynamics were obtained for gases sorbed by the adsorbent at the temperature of 20.2 K. The efficiency of using low-temperature adsorbent regeneration is shown for various temperature levels of cryogenic liquid [3]. Based on experimental research a chemical patron design is proposed. This makes possible the removal of hydrogen from the vacuum heat-insulating cryogenic tank cavity and monitoring the hydrogen absorption process according to the thermal chemical reaction effect.
Introduction
CSP belong to periodic operation devices — as an adsorbent becomes saturated, their speed of response reduces. As a result, the pressure in the vacuum cavity of the cryogenic tank is an increasing function of time.
For the complete reproduction of the ceolyte CSP absorptibility, a low-temperature adsorbent regeneration is used. The present work describes the possibility of using low-temperature regeneration for these purposes. It is assumed that for CSP operating at the temperature level of 20.7 K, the low-temperature regeneration will be a useful addition to the existing high-temperature regeneration method. For some particular cases, the low-temperature regeneration will just be the only possible tool that will allow avoidance of a number of emergency situations. The built-in CSP operating at 20.7 K are made as built-in models according to the design scheme [4, 5]. A similar pump layout, along with big advantages as compared with the side-mounted pump scheme (flange CSP), has one significant disadvantage. It is related to the necessity of discharging all cryogenic liquid to an empty vessel at the adsorbent regeneration. Additionally, the inner cryogenic tank cavity should be heated. For ceolyte CSP, the regen-
eration temperature should not be less than 200 °C. The factors enumerated above define large energy losses during the regeneration of big cryogenic tanks.
In the course of operation of big cryogenic tanks, a situation often arises when it is necessary to regenerate an adsorbent, but the component can not be merged into another vessel. Moreover, this could occur in two cases. The first case is as follows: the maintenance period has been completed, but it is to be extended at least for a short time. However it is impossible to prolong this period for the built-in CSP by means of conventional methods. The pressure in the tank HIC may arise up to the limiting level, at which the tank operation is forbidden. It may cause a high i evaporation capacity of the cryogenic liquid and even t lead to an accident. The second case corresponds to an | increased leak in the HIC. In this case, both hydrogen dissolved in the metal thickness and being released 3
T
through the defect pores and hydrogen being released | in the HIC through the defects from the cryogenic ¿; tank may take part in the gas release process. This | results in the super-saturation of the adsorbent. *
c
In order to overcome the enumerated situations, ° a method was proposed providing the low-tempera- 0 ture regeneration of the built-in CSP adsorbent [6]. This method allows regeneration CSP without merg-
Статья поступила в редакцию 06.11.04 г. Article has entered in publishing office 06.11.04.
Notation
B — the experimental constant, m3/kg;
CCSP — the thermal capacity of the CSP, J;
CINS — the thermal capacity of the SVHI, J;
CSP — the cryosorption pump;
D(x) — the diffusion constant;
e — the efficiency criterion regarding the cryogenic liquid storage method;
- ML
tym — m — the mass degree of the cryogenic tank filling with liquid;
Gins — the mass of the shield-vacuum thermal insulation, kg;
GT — the cryogenic tank mass, kg;
CT — the thermal capacity of the cryogenic tank, J;
CL — the specific heat of the cryogenic liquid, J/kg;
GCSP — the mass of the in-built cryoadsorp-tion pump with the adsorbent, kg;
HIC — the heat-insulating cavity;
L, L0, LC — the CSP absorptivity, with index "0" corresponding to the initial value and "C" — to the current value;
MH — the mass of liquid hydrogen together with the gaseous pad, kg;
M' — the passport liquid mass for the given tank, kg;
Mv — the mass of vapour, kg;
AMN t — the cryogenic liquid losses caused by the pre-term pressure pickling under the drainage-free storage, kg;
AMp — the evaporating liquid losses due to the molecular component of the heat inflows from the environment defined by the residual gas pressure in HIC, kg;
AMn — the cryogenic liquid losses due to the liquid trampling into an empty vessel while conducting the built-in CSP regeneration, kg;
AMQ — the evaporating liquid losses caused by the molecular component of the heat inflows from the environment defined by the pressure of the hydrogen residual gas component in HIC, kg;
Mi' — the mass flow-rate of the evaporating liquid per second, kg/s;
n — the degree of meeting the passport requirements regarding the CSP normal operation time;
N
G.C.
— the number of gas cushion replacements in the cryogenic tank;
PHIC — the pressure inside the heat-insulating cavity of the tank, Pa;
Pv P2 — the pressure values in the cryogenic tank, MI2 a;
PGC — the gas cushion pressure, Pa;
q — the differential heat of adsorption, J/(moleK);
QH2 — the intercrystalline hydrogen flux from the cryogenic tank casing, Pam3/s;
QH2 — the hydrogen flux produced by the gas release of intercrystalline hydrogen from the cryogenic tank metal as well as by fluxes through wall defects of the cryogenic tank and from the cryogenic tank due to diffusion through the wall, Pam3/s;
QH2 — the desorption hydrogen flux from the CSP adsorbent;
QHC — the cryosorption pump capacity as to hydrogen, Pam3/s;
QH2 — the chemical patron capacity as to hydrogen, Pam3/s;
dQe — the heat delivered to the cryogenic tank from the environment, J;
QL — the total heat inflow from the environment to the liquid, W;
Qj — the heat inflow per second caused by the molecular component of the heat inflows from the environment defined by the residual gas pressure in HIC, J/s;
QQ2 — the heat inflow per second caused by the molecular component of the heat inflows from the environment defined by the residual hydrogen pressure in HIC, J/s;
r — the evaporation heat, J/kg; Rg — the gas constant, J/(moleK); R(T) — the ratio of the specific adsorbent capacity at variable temperature to the specific adsorbent capacity at the temperature of 20.2 K, percent;
rV — the density of the cryogenic liquid vapour, kg/m3;
SVHI — the shield-vacuum heat insulation; tmp — the passport maintenance period of the CSP adsorbent, s;
tL — the time, within which the cryogenic liquid temperature in the cryogenic tank rises from
TL1 to T^ s;
Tj, T2 — the temperatures of the cryogenic liquid, accordingly, at the following pressures in the cryogenic tank: (Pp P2), K;
0 — the degree of the adsorbent saturation with gas indicating what part of the CSP absorptivity is spent: 0 = m/L, where m is the amount of gas absorbed by the adsorbent, Pam3;
tmtp — the actual time of the CSP turnaround period, s;
t — the current time lapsed from the moment of start of the low-temperature regeneration technique, s;
dU — the change of the inner energy of the system comprising the cryogenic tank with the cryogenic liquid, J;
v — the specific capacity of the adsorbent under the operating pressure, Pam3/kg;
v1, v2 — the specific adsorbent capacities, accordingly, at the following temperatures: (Tp T2), Pam3/kg;
VGC — the gas cushion volume in the cryogenic tank, m3.
ing the cryogenic liquid. The analysis of the possibility of using the low-temperature regeneration for CSP of cryogenic tanks of various temperature levels (96 K, 77 K, 20.7 K) has showed that it is applicable only the for hydrogenous built-in CSP.
Generation of a residual cryogenic tank atmosphere. Gas emission type influence upon CSP absorptibility
In Fig. 1, a cryogenic tank with the built-in CSP is shown.
In case of long periods of operation of big cryogenic tanks, the hydrogen gas emission of from the casing metal QH is of great importance.
Investigation of the opportunity to perform the low-temperature regeneration
Let's investigate the opportunity to perform the low-temperature regeneration of built-in cry-oadsorption devices on the basis of the widely spread specialised vacuum ceolyte CaEH-4B. Let us first discuss a configuration when the cryoadsorption devices are located inside a heat-insulating cavity within a big hydrogenous cryogenic tank with the cryogenic liquid supercharge. Let us consider a case of early adsorbent super-saturation with hydrogen. Based on the Henry equation one can express the desorption dynamics of gases absorbed by the adsorbent at the temperature of 20.2 K for the interval 20.2-32 K (Fig. 2).
100
R (T
Fig. 1. Cryogenic tank layout and illustration of gas release and gas absorption processes in a heat-insulating cavity where: 1 — outer casing, 2 — cryogenic tank with cryoagent, 3 — built-in cryoadsorption pump, 4 — chemical patron with gas absorbent, 5 — cryogenic liquid evaporator, 6 — drainage gaseous valve
Under normal CSP operation conditions, a residual atmosphere in the HIC is generated mainly at the expense of the gas emission components QH , QH . If the casing has a through air leak, then the flux QH O is critical for the CSP adsorbent. For a high magnitude of this flux, the residual HIC atmosphere may contain water vapours. They are partially frozen on the cryogen tank and also get into the CSP adsorbent (Fig. 1). In this case, the pores become locked by hydrated adsorbent cations. The CSP productivity drops sharply which leads to the pressure growth in the HIC. If there is a considerable leak QH O, the low-temperature regeneration will result in nothing. Only the high-temperature heating of the adsorbent pores under permanent HIC evacuation by auxiliary pumps will allow removal of water and restore the absorptibility.
Under normal CSP operation conditions, the residual HIC atmosphere is mainly represented by neon and helium. By the end of the maintenance period when QH drops sharply, the hydrogenous atmosphere is predominantly generated in the HIC. As is well known, the hydrogenous residual atmosphere, as compared with other possible residual atmospheres, is very undesirable, since it possesses the maximal thermal conductivity (see Section 10).
v = BPHICexp(-^)
= e
JL
д In
dT-1
Fig. 2. Gas desorption dynamics sorbed at the temperature of 20.2 K in the interval of the adsorbent temperature change of 20.2-32 K
It is known that in the region of the adsorption space filling 0 < 0,1 of the ceolyte CaEH-4B, the adsorbtion is defined by the Henry equation [7]:
(1)
and since q = const at T = 20-30 K, for T1 < T2 we shall obtain:
(2)
With the available family of adsorption isos-teres that are linear in the lnP - T-1 co-ordinates, the differential heat of adsorption q is defined by the tangent of the isostere incline in accordance with the Clapeyron-Clasius equation [8]:
(3)
v
2
For hydrogen in the region of 20-30 K:
q
-— 336,61. The desorption dynamics of gases
rg
sorbed under the temperature of 20.2 K within the interval of temperatures of 20.2-32 K is represented in the R(t) - T2 co-ordinates by a rather steep exponent (Fig. 2).
It is seen from the curve (Fig. 2) that 95 % of hydrogen sorbed at the adsorbent temperature of 20.2 K, is released under the adsorbent heating by 4.3 K and about 100 % — under the heating by 8 K. Here:
R(T) = -100 % . v,
R(T) —100• e ' T 20 2 , E = 20.2+32, (4) The efficiency of the low-temperature adsorbent regeneration is shown for various temperature levels of the cryogenic liquid (Fig. 3).
10 %
0.2 1
Oxygen vessel
Nitrogen vessel
Hydrogen vessel 20.2 K 32 K 77.36 K 104 K 90.18 K 120 K
Fig. 3. The adsorbent amount in a sorbent after desorption for various temperature levels of cryogenic liquid. Heating of liquid by thermal flow accumulation from the environment at the pressure increase from P = 1 atm to P„ = 10 atm
Low-temperature regeneration method
In [6], a method is proposed providing the pressure control in a vacuum cavity during the increase of the average cryogenic liquid temperature under natural growth of the gas pad pressure in a routine technological process and the desorbing hydrogen extraction QH3 (Fig. 1). Hydrogen is extracted by self-contained portable explosion-proof pumping devices on the basis of low-temperature chemical absorbers. The cryogenic liquid temperature changes achieve 5-6 K in routine technological processes and rarely — 10 K. The method makes it possible to continuously extract
hydrogen sorbed by the adsorbent and the shield-vacuum insulation surfaces located near the wall of the internal cryogenic tank. The punched SVHI layers serve as a sort of heat-protection shields that reliably protect the adsorbent against a "poisoning" action of such impurities contained in the pumped medium as H20, C02 and others [9]. The SVHI layers adjacent to the cryogenic tank appear as condensation-adsorption pumps, in particular, those of hydrogen. Hydrogen is pumped out by these layers in accordance with the cryosorption mechanism at gaseous condensates [10].
Hydrogen is removed from the CSP and the SVHI surface layers during the low-temperature regeneration in the process of the short-time (as compared to the maintenance period) growth of the average temperature of the thermodynamic system components. The system involves an inner cryogenic tank, a cryogenic liquid, a cryosorption pump and a thermal insulation. The average system temperature is increased by technological or artificial pressure growth in the gaseous pad of the tank. Moreover, the maximal heat supplied to the cryogenic tank from the environment is spent on changing the internal energy of the system: dQe — dU ;
dU = M Hj dU + GcapCcap dT +
(5)
As a result, the temperature of the liquid and that of the whole system will rise.
In Fig. 4, the dependence of the liquid hydrogen temperature on the pressure for drainage-free storage is shown.
40
K"
S 30-
20
10
8
2
1
0 1 2 3 4 5 6 7 8 9 Pressure in gas cushion P, atm
Fig. 4. Curve of liquid hydrogen temperature changes under the pressure increase in the gaseous pad
The time required to rise the cryogenic liquid temperature from TL to T^ is defined by the formula:
T,
'L 2
"J
T,,
M > CLdTL " ' - Tli) . (6)
Ql
Q,
After hydrogen is partially desorbed by the absorbent and removed by transportable pumping
devices, the average temperature of the cryogenic liquid is decreased by the gaseous pad draining. The liquid temperature is reduced in this case to 20.7 K. The cryosorption pump continues operating in the adsorption mode, with the degree of filling 0 being considerably less than before the regeneration. The SVHI layers located next to the cryogenic tank also have a lesser degree of hydrogen filling.
Experimental research
On the basis of full-scale experimental research dealing with the removal of residual hydrogen from the vacuum cavity of a big cryogenic tank, a chemical patron design has been proposed (Fig. 5). This design allows the transformation of hydrogen of the heat-insulating cavity of the tank into water, replace the chemical absorbent, activate it in the patron, evaluate the amount of absorbed hydrogen by the heat quantity released during the oxidation reaction and define the pumping termination moment.
Radiator
H
iL
■ e:
Thermopile
Radiator
course of the operation, during the intensive hydrogen release, the chemical absorbent temperature rises as a result of the exothermic hydrogen absorption. With the minimal thermal contact with the environment being provided (for example, by covering the chemical patron by a shell and fabricating a connecting pipe branch from a material with the minimal thermal conductivity coefficient), one may, to a certain accuracy, trace the hydrogen desorption from the CSP and the SVHI layers by recording chemical absorbent temperature changes in time [11]. So in [12], for the case of hydrogen being passed through a micaceous tube with a chemical absorbent weight (sample), the temperature grew up to 68 °C and then stabilised in the area of 35 °C.
Efficiency of the method
The efficiency of the method is defined according to a specially developed criterion specifying the value of relative losses of the cryogenic liquid:
3-
£ = where:
AMN t + AM P + 2AM n + AM,
N, t PH1C n
Qh
H2
M t
mp
aMn. = Pg.p.Vg.pPvNg
AMn
О tat
_ S¿\lmp
AMn » 0,1M 'ф ,
amQh2 =
О 2tat
¿^2 mp
n =
f
mp
~t±
Fig. 5. Chemical patron with a radiator for cooling a connecting flange packing and with thermocouples
In this case, the chemical patron is thermally insulated from the environment (the thermal insulation is not shown in the figure), and the chemical absorbent temperature changes measured by a thermocouple are documented by an analogue recorder.
Water being an oxidation reaction product is frozen out at the cryogenic surfaces. A chemical absorbent is activated at the activation test-bed having a direct temperature control by means of thermocouples. The absorbed hydrogen amount is monitored during the operating process by means of built-in thermocouples for lower temperatures. The chemical patron is installed at the object with a connecting nipple facing downwards (Fig. 1), and for the activation at the test-bed — with the chamber bottom facing the heating element. In the
(7)
When using this method, the value of relative cryogenic liquid losses will be minimal e< 1. Otherwise the relative loss factor will be il. In order to improve the efficiency of the chemical patron operation, a device was proposed [13] sustaining the temperature of a getter matter in the optimal temperature interval and providing the fire safety improvement.
Hydrogen cryosorption-desorption on gaseous condensates located at SVHI layers — an additional positive effect of the method
The gas absoption on a solid body surface by cryosorption is based on the interaction between molecules of the gas and the solid body. Adsorbents are those matters, which gas is bound with under the action of Van der Waals forces and which have higher characteristic temperatures, for example, higher melting temperature as compared with the adsorbed gas. The forces of interaction between the adsorbent particles and the gas ones are stronger than those of the intermolecular interaction of the adsorbent being in a condensed
state. With the temperature being increased, the adsorbent desorbs, with that being decreased — adsorbs again. It is known from [9] that gaseous condensates split at the SVHI layers. As the SVHI layers heat The most active component of a CO2 gaseous mixture desorbs last in the process of the SVHI layer warm-up. There are reasons to assume that this residual atmosphere component will be present in some quantity in the condensed state on the SVHI layers being adjacent to the cryogenic tank. Additionally, it is known that this component in a condensed state sorbs hydrogen very well [10]. The H2 adsorption isotherms on solid CO2 and other condensates are isotherms of the second type [14]. From the isotherm analysis of the hydrogen adsorption on solid CO2, one can see that under the operating pressure of 10-5 Pa in the vacuum cavity, the degree of filling a over hydrogen decreases by ten times as the SVHI temperature increases from 20 to 24 K [10].
These reasons show that in the heating-cooling process of the given thermodynamic system one should take account of the layers close to the SVHI. In the process of heating, they will lose some part of sorbed hydrogen and release the sorption space to absorb hydrogen as the thermody-namic system "cryogenic tank-CSP-SVHI" cools. Theoretically, for minor filling, the process should meet the Henry law.
Apart from CO2, with regard to the adsorption capability, the following condensates [10] may be listed:
O2, C3H8, NH3, Ar, N2, C„Hfi, CH4.
The implementation of the low-temperature regeneration and, as a consequence, the cryogenic tank thermocycling in some insignificant interval of temperatures leads to thermocycling of all SVHI layers. However only near-wall SVHI layers will thermocycle with the maximal amplitude. It is these layers that will contribute maximally to the formation of the hydrogen pumping process.
Thus, for the low-temperature regeneration, one should also take account of the SVHI layers as an additional "cryosorption pump".
The last conclusion recalls a concept of "a non-isothermal condensation-adsorption pump" by G. G. Zhun' [9]. A great number of works [15, 16] are devoted to the influence of condensed gases on the efficiency of the laminated vacuum insulation.
Apparently, a certain positive contribution into the increase of the adsorption volume at the implementation of the method will also be made by the adsorbent reallocation in the ceolyte pores according to the mechanism described in the references [17].
Isothermal diffusion with mass sources
In order to get a variational formulation of a mathematical model of the molecular heat and mass transfer process in the SVHI, we shall use the
main variational principle of the classic phenome-nological thermodynamics [18].
Let us formulate a task of evaluation of the SVHI layers contribution into the overall picture of hydrogen desorption after the cryogenic tank is heated and hydrogen absorbed following the cryogenic tank cooling. We expect that the solution of this task will give the concentration of residual gas in the SVHI as a function of the spatial coordinate and time for the stationary temperature field. For this purpose, let us formulate a varia-tional non-linear non-stationary problem of diffusion with mass sources being distributed over the volume for the molecular mode of flow of one-component gas being pumped out in the direction transverse in respect to the insulation layers. Due to a long cryogenic tank diameter, let us assume, to simplify the model, that the insulation layers are plane. Let us consider, for the first approximation, that the temperature field being in thermal insulation with the thickness of l is preset and stationary. Then the effective diffusion coefficient depending on the temperature will be a function of the spatial co-ordinate (x, or X = x/l). The desorption velocity that in this problem defines the specific volumetric power of distributed mass sources depends not only on the temperature but also on the changes of the gas concentration velocity at the given point [19]. Since there is some space in the SVHI package where the hydrogen desorption-absorption processes occur most intensively, then there is the most active zone of hydrogen cryosorption on gaseous condensates in the near-wall (the coldest) zone. The desired gas concentration function in this zone is known, as it is equal to the equilibrium adsorbent (hydrogen) concentration, i.e. is defined by a degree of as(x) surface filling:
as (x) =
number of molecules adsorbat _ Qadsorbat
number of molecules adsorbent Qad
The hydrogen concentration for the temperature in the given cross-section point of the package is equal to Cs(x). On this basis, the region of the problem solution may be limited by the warmest part of the thermal insulation where the intensity of the hydrogen adsorption-desorption process equals to zero: x e [0, la(t)] for insignificant SVHI temperature deviations.
The velocity of movement wa(x) of the adsorption-desorption zone boundary la(x) will be defined from the equation of balance:
0c dc
cawa = D(T--"Г X x = la
ox ax
(8)
where ca(x) — specific volumetric (effective) condensate concentration.
With regard to the remarks made above, the differential mathematical model of the problem has the following form:
дс __д■ дт дх
D( x)
дс дх
= z ( x)
дс дт '
12 11
X e (0, la (t)), T = (0, ~); c(0, t) = cH (t), c(la (t) = Cs (lfl (t)),
t
c(X, 0) = c„ (X); where /, (t) = j w, (t)dt (9)
0
This task is solved by the final element method over the spatial variable and by the finite difference method over time.
The contribution of the hydrogen in the total heat-conductivity of heat-insulation in vacuum area possible to value at the diagram (Fig. 6).
36% Hydrogen
5%
Nitrogen
%
Oxigen
3%
3 % Carbon dioxide
Water Arg°n
Fig. 6. Thermal conductivity coefficient for various gases, W/(mK)
In order to obtain the variational formulation of the problem, let us apply the variational principle to models of molecular heat and mass transfer processes in continuum with the account of internal sorption processes described in [20]. Besides, let us use the method of transition from varying over chemical potentials to that over microsystem component concentrations stated in [20]. Since in accordance with the boundary conditions of the problem a variation of the concentration at the boundaries of the solution region equals to zero, a variation mathematical model of the problem can be expressed as follows:
'la ( T)
SJJ
. дс ^ , . дс дс
--D ( x )--
дт дх дх
dxdT = 0 (10)
The desired solution may be approximated by a system of linear splines [20] with the non-uniform step of the spatial area partition [21].
Implementation of the method providing minimal temporal and economical expenses
An idea to reduce temporal and economical expenses at the implementation of the method implies the improvement of the technological process proposed in [3, 6], namely, filling the vacuum cavity with hydrogen in the amount calculated or defined automatically through a precision leak, for example, as in [22, 23, 24]. In Fig. 7, a vacuum leak is illustrated supplied by a special precision drive [22].
Fig. 7. Guided vacuum leak with a hydraulic reducer, where: 1 — heat-insulating casing, 2 — regulated throttle, 3 — closing element in the form of a conical needle,
4 — threaded regulator of the conical needle location,
5 and 6 — big and small bellows of the hydraulic reducing gear, 7 — working liquid, 8 — movable face of the big bellows, 9 — movable face of the small bellows, 10 — saddle, 11 — chamber for the nut movement limit, 12 — regulating nut, 13 — washer, 14 — check nut
The main idea of the device under consideration is as follows: in order to reduce an influence of the instrumental device error on the needle movement accuracy and to improve the precision of setting the required gap at the expense of reduction of the transfer constant of rotational movement of the nut into the progressive movement of the needle, the threaded mechanism of the conical needle movement is related with the needle indirectly via the second needle location regulator (hydraulic reduction gear) with a prescribed transfer constant.
The leaks [22-24] provide the automatic filling of the vacuum heat-insulating cavity with hydrogen up to the prescribed pressure in case of the availability of a feedback with the pressure gauge in the HIC, the level gauge or the temperature meter for peripheral liquid layers. In this case, hydrogen is not practically absorbed by the CSP, as the adsorbent has already been saturated by hydrogen. With the hydrogen concentration being increased, due to its super-high thermal conductivity as compared with the rest of the gases of the residual atmosphere, the heat inflows towards the cryogenic liquid increase sharply.
The peripheral layers are heated up more rapidly. The time tl defined by formula (6) will be significantly less than in the technique [3, 6]. It should be noted that at the implementation of the method, the devices for the temperature stratification (inhomogeneity) elimination [25], for example, [26], of the cryogenic liquid should be stopped.
Conclusion
The method allows the provision of the efficient use of technological measurement of the average cryogenic liquid temperature observed during the routine cycle of storage, refuelling and extracting the component for conduction of a "cold" regeneration of the built-in CSP with no evacua-
tion of the cryogenic tank. In some cases, in order to eliminate the HIC emergency mode of the cryogenic tank, it is expedient to perform the artificial cryogenic liquid thermocycling by varying gaseous pad pressure.
Using the method one may reach a significant reduction of power and operation expenses. The cry-oagent losses are reduced in the process of regeneration at the expense of excluding routine operations on the tank evacuation and its heating with considerable losses of liquid hydrogen under its necessary displacement into the empty tank and backwards. The implementation of the method will significantly increase the passport maintenance period of the CSP operation. The method is useful for the operation of large cryogenic facilities with a tendency in their development towards unmanned technologies.
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