9. LPOOL

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General introduction

The LPOOL model simulates the time-dependent evaporation of a multi-component liquid pool on land or water. The pool can be boiling or non-boiling. Dikes can be modelled as well. The pool is assumed to be well-mixed (no concentration gradients within the pool).

LPOOL replaces the EVAP model as available in previous version of HGSYSTEM. The program is functionally the same as the LSM90 model, developed by Exxon Research & Engineering Company.

Apart from the evaporating pool calculations, LPOOL can calculate liquid spill rates from a reservoir, using either a choked flow equation or a Bernoulli liquid flow equation. The user can specify prescribed spill rates, if required.

Range of applications and limitations

For more details on the validation of the LSM90 model, see the original LSM90 references in the Technical Reference Manual chapter on LPOOL.

Like the EVAP model, LPOOL can not model the full HF chemistry and thermodynamics. However, similar to the EVAP model, it can do a post-HFSPILL run using the relevant physical properties of HF.

LPOOL is a fully time-dependent code, it can not be run in steady-state mode. Therefore only a link file to the time-dependent dispersion model HEGADAS-T is created by LPOOL. If the user judges that the pool evaporation can be represented by a steady-state release, a HEGADAS-S input file can be prepared based on the example input files available in the HGSYSTEM\STINPUT subdirectory.

LPOOL is intended to be used for evaporating liquid pools. If the mixture at reservoir conditions (also) contains compounds which are always vapour-only (e.g. nitrogen, oxygen, methane), numerical problems may occur or results may be incorrect. Only include in the mixture specification those compounds (GASDATA input block) which will form part of the liquid pool upon release.

Guidance for use

If numerical problems occur during LPOOL runs, changing the input parameters slightly might help. Also check that the input data is consistent. See remarks for specific keywords below. HEGADAS-T will print a warning if the spill data from LPOOL imply that the pool has not dried up completely at the end of the simulation time. The user can try to find values for MAXTIM and DTLINK (see below) so that a complete pool description is obtained.

The report file 'casename.LPR' contains a reprint of the input data and a summary of the average pool evaporation results. The file 'casename.LPT' contains time-dependent results like evaporation rate and mass in pool. The file 'casename.LPC' shows the composition of the cloud above the pool as a function of time (molar and mass fractions, all compounds) and 'casename.LPS' gives the same information for the pool mixture.

LPOOL INPUT PARAMETERS

A description of all the input parameters that can occur in a LPOOL input file will be given.

The LPOOL input file has the DOS filename 'casename.LPI' where 'casename' is the user-supplied name of the problem.

In the following, actual keywords are given in capitals and in bold. The descriptions of less important parameters or parameters that need not normally be set by the user, are given in a smaller font.
All parameters, except TITLE, occur in blocks preceded by a specific block keyword. For LPOOL these block keywords are: CONTROL, SPILL, RESERVOIR, GROUND, GASDATA, FLASH and AMBIENT.

The TITLE keyword does not occur in a parameter block.

TITLE The title of the current problem to be run with LPOOL.
At most 50 alphanumeric characters.
Optional, no default.

The CONTROL input block contains several general control parameters.

MAXTIM Maximum simulation time for this LPOOL run (s).
0.1 <= MAXTIM <= 1010
Mandatory.
MINFILM Minimum (film) thickness of pool (mm = 10-3m )
Optional, default is 1 mm.
Although simulation results do depend on the value of MINFILM, its precise value for any given compound is unfortunately rather insecure. Theoretically it should never be lower than the capillary depth hc= SQRT{ SIGL/ (g x rhoL) }
where SIG L is the surface tension (N/m), g the gravitational acceleration (9.8 m/s2) and rhoL the liquid density (kg/m3). Usually MINFILM is taken to be order hc.
DTLINK Time step for pool data in HEGADAS-T link file (s).
0 <= DTLINK <= 104
Optional, default is 20 s.
LPOOL creates a link file for HEGADAS-T which contains pool data printed at time intervals of DTLINK s. The maximum number of pool data records that HEGADAS-T can use is 100. It is probably necessary to run LPOOL at least once to be able to find a value of DTLINK that generates sufficient pool data records for HEGADAS-T so that a good representation of the pool history is communicated to HEGADAS-T.

The GROUND block contains the parameters which describe the ground composition and the dike composition and size (if present).

Optional, default is 0 (indicating no dike).
GRCOMP Ground composition (-).
GRCOMP = 1, 2, 3, 4, 5. 6 or 7.
Optional, default is 3 (concrete).
The possible ground surface materials are:
1: wet sand
2: dry sand
3: concrete
4: insulated concrete
5: steel
6: insulated plastic
7: water
GRTEMP Ground surface temperature (Degrees C).
-50 <= GRTEMP <= 50.
Mandatory.
DIKEPRES Dike (bund) presence indicator (-).
DIKEPRES = 0 (no dike) or 1 (dike).
Optional, default is 0 (no dike).
DIKECOMP Dike composition (-).
DIKECOMP = 0, 1, 2, 3, 4, 5. or 6.
1: wet sand
2: dry sand
3: concrete
4: insulated concrete
5: steel
6: insulated plastic
Only relevant if DIKEPRES = 1.Will be set to 0 if DIKEPRES = 0.
DIKEHEIGHT Height of dike (m).
0 <= DIKEHEIGHT <= 10 3
Mandatory if DIKEPRES = 1.
DIKERADIUS Radius of dike (m).
0 <= DIKERADIUS <= 103
Mandatory if DIKEPRES = 1.

The SPILL block contains the parameters which describe the discharge details for a release of liquid from a reservoir.

SPTYPE Spill rate type (-).
SPTYPE = 0, 1 or 2
Mandatory.
SPTYPE = 0 indicates a fully user-specified spill rate using the SPILDATA parameters below.
SPTYPE = 1 indicates that LPOOL will use a choked flow model to calculate the discharge rate. In this case PRES must exceed PATM!
SPTYPE = 2 indicates that LPOOL will use a standard liquid Bernoulli relation to determine the spill rate.
CD Spill discharge coefficient (-).
0.0 <= CD <= 1.0
Optional, default is 0.6.
DURATION Spill duration (s).
10-6<= DURATION <= 105
Optional, default is MAXTIM + 100.
Specify only if spill stops before exhaustion (e.g. to simulate plugging of leak). Otherwise set larger than MAXTIM. Normally LPOOL calculates spill duration.
Not relevant if SPTYPE = 0.
SPILDATA User-specified spill rates and durations.
Mandatory if SPTYPE = 0.
  The SPILDATA keyword must be followed by two parameters (#1 and #2):
#1 spill rate (m3/s)
0 <= #1 <= 106.
#2 spill duration (s).
0 <= #2 <= 106.
The SPILDATA keyword with its pair of parameters can be specified up to five (5) times.
Only relevant if SPTYPE = 0.

The RESERVOIR block contains the parameters which describe the reservoir (tank) containing the liquid to be released. The reservoir is assumed to be a vertical cylinder.

TRES Temperature of the reservoir fluid (Degrees C).
-270 <= TRES <= 500.
Mandatory.
PRES Absolute pressure within the reservoir (atm).
0 <= PRES <= 200.
Mandatory.
PRES must be equal or larger than the ambient pressure PATM. For a vented tank they will be equal and in this case the only driving force for the spill is the liquid height.
If SPTYPE = 1, then PRES must exceed PATM.
RRADIUS Radius of the cylindrical tank (m).
10-6 <= RRADIUS <= 103.
Mandatory.
RRADIUS must not exceed DIKERADIUS of the GROUND block.
RFLHEIGHT Initial fluid level in the cylindrical tank (m).
10-6 <=RFLHEIGHT <= 103.
Mandatory.
Must be larger than ZEXIT.
DEXIT Equivalent diameter of reservoir (tank) orifice (m).
10-6 DEXIT 103.
Mandatory.
ZEXIT Elevation (height) of orifice (m).
0 <= ZEXIT <= 103.
Mandatory.
ZEXIT must be less than RFLHEIGHT.
ZEXIT must be greater than DEXIT/2.
  N.B. Both RFLHEIGHT and ZEXIT are measured with respect to ground level

AMBIENT block contains parameters describing the conditions of the ambient atmosphere.

TATM Ambient air temperature at height 10 m (Degrees C). -50 <= TATM <= 100.
Mandatory.
UATM Ambient wind velocity at height of 10 m (m/s).
1.0 < UATM <= 20.
Mandatory.
PATM Ambient air pressure (atm).
0.7 <= PATM <= 1.1.
Optional, default is 1.0 atm.
PATM must be less than or equal to PRES of the RESERVOIR block.
RHPERC Relative air humidity (%).
0.0 <= RHPERC <= 100.
Optional, default is 70 %.
  Used in aerosol calculation and to write HEGADAS-T link file.
CLCOVER Fraction of sky covered by clouds (-)
0.0 <= CLCOVER <= 1.0.
Optional, default is 1.0.
SPSTART Spill starting time (24 hour clock)
0.0 <= SPSTART <= 24.0
Optional, default is 12.0.
SUNRISE Sun rise (24 hour clock)
0.0 <= SUNRISE <= 24.0.
Optional, default is 6.0.
SUNSET Sun set (24 hour clock)
0.0 <= SUNSET <= 24.0
Optional, default is 18.0.
Note: SPSTART, SUNRISE and SUNSET are decimals indicating time using a 24 hour clock. Example: 7:30 am is given by 7.50 and 7:15 pm is 19.25.

FLASH block contains parameters concerning the flashing and aerosol formation of the spilled liquid.
FLASHFRAC User-specified flash fraction (-).
0.0 < FLASHFRAC <= 1.0.
Optional, default is 0.
  Only used if AUTOFLASH = 0.
AEROSFRAC User-specified aerosol fraction (-).
0.0 < AEROSFRAC <= 1.0.
Optional, default is 0.
  Only used if AUTOAEROS = 0.

The GASDATA block contains the fluid composition and thermodynamic data. LPOOL will always assume the tank contains (some) liquid and the calculations will always use two-phase thermodynamics. Tanks containing only vapour can not be modelled.
A mixture containing some volatile compounds which are vapour-only at reservoir conditions (e.g. methane, nitrogen) may cause numerical problems or give incorrect results. Only include in the mixture specification those compounds which will form part of the liquid pool upon release.
Using the HGSYSTEM module DATAPROP to find the values for GASDATA parameters is strongly recommended.

WATERPOL Mole fraction water in fluid (-).
0 <= WATERPOL <= 1.0.
Optional, default is 0.0.
CPGAS Specific heat at constant pressure of fluid without water (J/(mole K)).
5 <= CPGAS <= 300.
Mandatory for writing the link file to HEGADAS-T.
Thus in practice CPGAS must always be specified. Using the HGSYSTEM module DATAPROP to find CPGAS is strongly recommended.
MMGAS Molar mass of FLUID without water (kg/kmole).
2 <= MMGAS <= 200.
Same comments as for CPGAS apply. Again, use of DATAPROP to calculate MMGAS is recommended.
HEATGR Natural convection heat transfer group
5 <= HEATGR <= 100.
Same comments as for CPGAS apply. Again, use of DATAPROP to calculate HEATGR is recommended.
SPECIES Fluid component properties.
Contrary to other HGSYSTEM modules (SPILL, HEGABOX, AEROPLUME and HEGADAS) LPOOL always uses two-phase thermodynamics. Vapour-only calculations are not possible. It is assumed that the tank always contains (some) liquid.
The SPECIES keyword plus parameters must be specified for every compound in the fluid mixture, except water. The sum of the molar fractions used in the SPECIES (see parameter #2 below) must equal 1.0 - WATERPOL.
Again, the use of DATAPROP to generate the input parameters when the SPECIES keyword is being used, is strongly recommended.
Currently a maximum of 8 components can be specified (excluding water). Please note that DATAPROP allows for more compounds to be specified. DATAPROP also splits dry air (if specified) up into nitrogen and oxygen, thus generating two compounds instead of one. Thus the LPOOL link file generated by DATAPROP could contain the SPECIES keyword more than 8 times. The user should combine or remove compounds if this occurs.
Within the above-mentioned restrictions, there are no restrictions within LPOOL concerning the number of aerosols forming or the number of compounds per aerosol. Please note that HEGADAS does have restrictions: either a single two-compound aerosol or a number of separate one-compound aerosols are allowed (not regarding water and dry air), other combinations are not supported.
Following the SPECIES keyword of a certain compound a block of 16 parameters (#1 to #16) must be specified:
#1 compound name (maximum of 12 characters).
#2 mole fraction in fluid mixture (-).
0<= #2<= 1.
#3 ;aerosol class (-).
-1<= #3 <= 50.
#4 specific heat of vapour (J/(mole K)).
5<= #4 <=300.
#5 specific heat of liquid (J/(mole K)).
0<= #5 <=103.
#6 heat of vaporisation (J/mole)
0<= #6 <=105
#7 critical temperature (K).
0<= #7 <=104
#8 critical pressure (atm).
0<= #8 <=103
#9 vapour pressure function coefficient B1.
-108<= #9 <=108.
#10 vapour pressure function coefficient B2.
-108 <= #10 <= 108.
#11 vapour pressure function coefficient B3.
-108 <= #11<= 108.
#12 vapour pressure function coefficient B4.
-108 <= #12 <= 108.
#13 molar mass (kg/kmole).
2 <= #13 <= 200.
#14 liquid density (kg/m3).
1<= #14 <= 105.
#15 normal atmospheric boiling point (K)
0<= #15 <= 104.
#16 vapour viscosity (Pa.s = kg/m/s)
0<= #16 <= 105.
Note: the saturated vapour pressure of the compound is described by the Wagner function:

Pv (T) = Pc x exp { [ B1 x Q + B2 x Q1.5 + B3 x Q3 + B4 x Q6 ] / Tr }
where T is the vapour temperature, Pc the critical pressure, Tc the critical temperature, Tr = T/Tc and Q = 1 - Tr.

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