Fixed Roof Storage Tanks

Fixed Roof Storage Tanks

       Many chemical facilities locate storage tanks in a common area referred to as a tank farm.  For example, tanks are needed when a manufacturing process involves a large throughput of solvent and the production facility is operated for extended periods of time during the year.  In this case, large storage tanks may be used for holding the fresh solvents.  Additionally, such chemical processes tend to generate high volumes of crude or spent solvent that must be further processed by distillation or some other purification technique.

       Emissions from solvent storage tanks normally originate from transfer operations when solvent shipments are received from suppliers and from breathing losses due to daily fluctuations in temperature.  Storage tank emissions are calculated for the total time that the tank contains the specified solvent.  In many cases, a storage tank may hold the same solvent for the entire year.  This situation is different from the typical chemical process, which involves many batches or production lots with each batch requiring only a few days to complete. 

       Emission Master provides modeling for vertical cone top, vertical dome top, horizontal, and isothermal (or underground) vessels.  The specific type of storage tank calculation model used by the program is determined by the type of storage vessel that has been chosen from the Equipment Database at the time that the model has been defined. 

An explanation of the data entry fields and requirements are described as follows:

· Activity Title: Enter a single line of text as a brief reference to the process step being created which will be used by the program as a Title Page entry.

· Vent I.D. Field: If the vessel, condenser, or other control device vent contains a vent identification number or code then this information may be entered in this edit field or selected from the drop down list.

· Equipment: This button is used to access the Equipment Database to select a vessel or similar equipment item for use with this processing model.  Only a vertical cone top, vertical dome top, horizontal, or isothermal storage tank may be chosen for the storage tank model.  Storage tanks contain additional fields such as the paint color, conservation vent setting, which are required to satisfy the modeling requirements. 

· Climate: Select this button to access the Climate Database and select the local climate data.  The average atmospheric pressure will be displayed in the Pressure box. 

· Start & End: Activate the Start and End drop down controls to configure the beginning and ending dates for the storage tank usage.  The calculated duration will be displayed in days. 

· Period Throughput: The period throughput volume for the process mixture is used in calculating the working losses from the storage tank during the usage period.  Once entered, Emission Master will offer to spread the volume throughput uniformly across the period based on the number of days in each month. 

· Crude Oil Factor: Enter any crude oil factor that might be associated with the material being stored.  In most cases this value will be 1.0.

· Contents: If this is the first time that a vessel is being used in the process file then it will be shown as empty.  However, if the vessel has been featured during an earlier step of the current process then the initial contents box will display the resulting mixture from its last operation.  Press the Edit button to define a new mixture or to modify an existing one that might be shown.  Press the Clear button if it desired to reset the initial contents to be empty.  Press the Mix DB button to import a mixture description from the currently connected Process Database.  If the storage tank is a vertical cone top or dome top vessel then the contents volume should be adjusted to be equal to the average daily contents for the period.  However, if the storage tank is a horizontal vessel then the average daily contents volume is automatically defined by the EPA breathing loss model to be 50% of the vessel capacity. 

· Control Devices: A control device is an equipment item which, when installed in the process vent line, reduces the level of certain compounds in the final gas stream.  Control devices are selected from the connected Controls Database.  The Storage Tank Model allows for multiple control devices to become part of the venting scheme for the source vessel.  Press the Controls button access the main Controls Database interface.