bbox2 is an extension CavBox. It is a numerical simulation program for gas storage in salt caverns or porous media. For gas storage in porous media the program has an interface to TOUGH2.
bbox2 simulation of porous media storage
Simulation corner point grid with pressure [bar]
during gas production
bbox2 simulation of salt caverns and surface facilities
Below the currently implemented modules for the simulation of the storage process are listed:
Gas / Equations of State
In principle, any gas or mixture of gases can be used as the working medium. However it is recommended to use inert gases (with respect to corrosion), such as nitrogen or natural gas. Natural gas is particularly suited due to its molecular structure and the resulting high heat capacity. Whereby if air is used as a working medium, corrosion to the plant facilities due to oxygen will occur over time, and thus components will need to be replaced at some point with related additional costs.
For the calculations, the composition of the gas must be specified. All common components including water can be used. The z factors, heat capacities, adiabatic exponent and dissolved water are calculated with the standard Equations of State.
The water dissolved in the gas is calculated in terms of possible formation of gas hydrates.
For the calculations of the state in the caverns the knowledge and experience gained during the past several decades in natural gas storage is implemented , all relevant operations such as convergence or heat conduction are included.
Pressure losses and head temperatures are calculated for the cavern wells. Several wells per cavern can be defined.
The loss of any pressure and/or temperature changes are calculated for the pipes.
Free Water Separator (FWS) / Free Water Knock-Out (FWKO)
The amount of water that is released at a certain temperature and pressure within the gas is calculated, so that the free water can be removed from the gas stream.
The compression of the gas can be achieved through several varying specifications. Either the outlet pressure or the outlet temperature can be specified. The compressor can also be operated in a way that the outlet pressure is equivalent to the well head pressure of the low pressure cavern. Pressure, temperature and water content are calculated as well as compression energy, power and other relevant parameters.
The calculations in the expansion turbine are similar to those during the compression.
Heater/Cooler with heat storage
The gas flow can be cooled or heated. A heat storage facility can be connected to the heater/cooler, where the heat is stored during compression and accordingly during expansion can be fed back into the gas stream.
The gas flow can be split and/or merged again using splitter and jointing technology. This subsequently allows either the use of 2 parallel wells in a cavern or several compressors simultaneously.
The gas flow can be throttled to adapt to any existing restrictions in natural gas storage operations.
Simulation of an erneo bulk storage example. Calculation of state in caverns and surface facilities.