Heat Transfer Agents
A heat transfer agent is an agent used to carry out a heating or cooling task as required by the performance of the unit procedure. Demand for heat transfer agents is calculated by operations that perform heating or cooling. SuperPro Designer keeps track of the instantaneous as well as cumulative demand of heat transfer agents.
Auxiliary utilities can also be specified for each operation to account for any cooling or heating consumption that is not currently computed by the simulation model. You can set the auxiliary utilities for an operation through the Operations Dialog: Labor etc. Tab. When auxiliary heating and cooling are specified, the provided values are not used in heat balances. They are only used in calculating the total utility consumption and the operating cost of that operation (and the associated equipment).
Energy Recovery
The demand for heat transfer agents may be reduced by recovering the energy from operations needing cooling and matching it with cold operations which require heating. For more details on recovering energy in SuperPro Designer see the Energy Recovery topic.
Definitions in the System Database and in the User Database
The ‘SuperPro (User)’ database contains the agent databank and it currently has a limited list of options for heat transfer agent types. To review the list of such available agents, select } from the main menu (or hit F3 as a shortcut). This will bring up the Heat Transfer Agents Databank Dialog. Users can add to this list by including their own definitions for heat transfer agents. Changes made to the heat transfer agents databank do not affect existing process files or other parts of the databank even if the edited heat transfer agents are used as the basis for utilities declared in sites.
For more details on the Heat Transfer Agents Databank, please see Heat Transfer Agents Databank.
Registered (in Use) Heat Transfer Agents
When selecting a heat transfer agent for an operation, you can choose from a list of generic-type agents defined in the Heat Transfer Area databank or, for operations in procedures owned by allocated sections (see Section Allocation), you can choose from the corresponding site utilities. Agents currently in use can then be inspected from the List of Heat Transfer Agents Currently in Use dialog accessed by selecting } } } or } } from the main menu. From here you may edit the properties of a heat transfer agent or you can reset its properties to match the values as kept in the ‘SuperPro (User)’ database. See Heat Transfer Agent Properties.
If at any time the user wishes to change the Heat Transfer Agent used in the process with another agent, instead of visiting all the locations the agent is used and replacing it, the Replace Resources Dialog can be used to perform a global switch of resource(s) with another resource(s).
Heat Transfer Agents in Sites
To add, edit or delete heat transfer agents declared as utilities in sites, select } from the main menu. From the Sites & Resources Databank Dialog that appears, you can select the desired site from the left pane (site tree) and the utilities node on the right pane and you may add new, edit, or delete heat transfer agents by clicking on the appropriate button from the toolbar.
When adding a new site utility you will be presented with a dialog which displays all currently available heat transfer agent definitions in the agent databank. From there you can select one or more agents that you want to include in the site.
Once a heat transfer agent is added to a site as a site utility then you cannot delete it from your agent databank; first you must remove the agent from the site and then you are free to delete the agent from your agent databank.
If a section is allocated to a site, then available to operations of this section are not only utilities of this site but of its parent sites as well. This implies that if there is a central utility plant in a site then all produced utilities are available to all sub-facilities within that site.
Changes made in site utilities may affect existing process files (opened or closed at the time of the modification) that contain sections that use them. SuperPro Designer will not attempt to reconcile any process files currently not open in by the program. However, SuperPro will require that any open process files be consistent with the state of currently available resource databanks. Therefore, all changes done in the site and resources databank will automatically be propagated to open process files even if de-allocation (i.e. substitution with generic-type utilities) is needed to maintain consistency. Such changes could affect both material balances as well as economic results so re-solving M&E balances might be needed for all affected process files.
For more details, see Adding or Deleting a Heat Transfer Agent.
Heat Transfer Agent Properties
The parameters of a heating/cooling agent as shown in the heat transfer agents databank are the default parameters that are used the first time any of the processing steps in your process file employs that heating/cooling agent. If you decide to use different values for your specific process file, then you can adjust those parameters without affecting the default values of the agent in the databank, by bringing up the List of Heat Transfer Agents Currently in Use that appears when you select the } } option from the main menu, or just the } option from the flowsheet context menu. The dialog that pops up displays a list with all heat transfer agents currently employed by the process file.
To view or edit the properties of a heat transfer agent, you should click on the agent's index column to select it and then press the View/Edit Properties button (
). Alternatively you can double-click on the agent's index column. The Heat Transfer Agent Properties Dialog that comes up contains the agent's data organized in three tabs. Changes made in the heat transfer agent through this dialog will only affect this process file; they will not be stored in the Heat Transfer Agents databank. If you want the agent in this process file to take up the properties of the agent in the databank (in case they are different) select the agent by clicking on the agent's index column and press the Update Properties from DB Record button (
). If you want to update the databank's record (heat transfer agent properties) based on the current process file's record press on the Update Properties in DB button (
). If you wish to deposit the selected agent to the databank, then click on the Deposit Record in DB (
) button.
The Properties tab lets you define the type of the agent (heating or cooling), the temperature at which the agent is available from the utilities support plant, the temperature at which it should be returned to the utilities plant, and the unit cost charged for the use of this agent, which can be specified either on a mass basis (e.g., in $/MT of heat transfer agent mass) or on an energy basis (e.g., in $/kcal of heat transfer agent energy change). Note that only through the databank you can change the type of an agent and, as mentioned before, even if you do that, that change will not affect process files that make use of this agent.
The Availability Limits tab lets you define bounds on consumption of this agent. There are two types of limits: rate limits (instantaneous or time-averaged over a user-defined time span) and cumulative limits over a user-defined time span. Upon request, these limits will be plotted on the resource consumption charts (see Heat Transfer Agent Consumption Chart) so that you can compare them against the actual consumption.
The Inventory Data tab lets you define storage and supply data for this agent that, in turn, will be used to calculate the inventory chart lines (see Heat Transfer Agent Consumption Inventory Chart). This tab is displayed only when the heat transfer agent has been defined to be storable. This is done by editing the corresponding check box in the Heat Transfer Agents Properties tab. No inventory charts can be created for non-storable agents.
Note that, for site utilities, data in the Properties and Availability Limits Tab are not editable through the Heat Transfer Agents Currently in Use dialog. The reason is that site utilities could be shared by different process files and only through the site databanks their properties can be modified. To edit those values, you will need to visit the sites databank through the } menu item as explained before.
The locations where a heat transfer agent is currently utilized in the process can be viewed by clicking on the button 
. This can be in operations, which are displayed in order of first use accompanied with their hosting procedure.
Unit Cost of Heat Transfer Agent
Note that the annual demand of a heat transfer agent that you see, for example, on the List of Heat Transfer Agents Currently in Use dialog, indicates the annual amount of heat transfer agent used by the flowsheet’s processes, not the annual amount of heat transfer agent that you need to buy every year. That is because the heat transfer agents are supposed to be recycled to the utility plant and not spent (wasted) in their entirety (see ). Similarly, the unit cost of heat transfer agent is supposed to indicate how much it costs (per unit mass or energy) to get the required amount of heat transfer agent ready for use by the flowsheet’s processes, not how much it costs on a unit mass or energy basis to buy the required amount of heat transfer agent (unit purchase cost).
For example, consider the case of several cooling procedures where glycol is used as cooling agent. The utility plant is supposed to supply the chiller with 100 MT/yr of glycol at a supply temperature of -10°C, and the glycol is supposed to return to the utility plant at a return temperature of 0°C. It is also assumed that 5 MT/yr of glycol are somehow lost along the way of glycol usage, or during the regeneration process of glycol.
The life cycle and unit cost of a heat transfer agent.
Therefore, only 95 MT/yr of glycol are fully recirculated between the utility plant and the processing plant. In that case, the utility plant must spend money for two items:
a) to buy 5 MT/yr of fresh glycol, and
b) to bring the total amount (100 MT/yr) back to the required supply temperature (-10°C).
The unit cost on a mass basis of the heat transfer agent can be calculated by dividing the total annual cost of the utility plant (the sum of "a" and "b") by the agent's annual demand. In mathematical terms, we can write:
mt * Ct = (mf * Cf) + (mt * Ce)
Or, equivalently
Ct = (mf/mt * Cf) + Ce = Cf' + Ce
Where:
mt is the total agent demand (in MT/year)
mf is the fresh agent demand (in MT/year)
Ct is the total unit cost of agent used (in $/MT of total agent used)
Cf is the unit purchase cost of fresh agent (in $/MT of fresh agent used)
Ce is the unit cost of energy consumed by the utility plant (in $/MT of total agent used)
Cf' is the fresh agent cost per unit amount of total agent used (in $/MT of total agent used)
It is possible to calculate the cost Cf' if you associate the heat transfer agent with a particular material (pure component or stock mixture). As an example, the "Glycol" heat transfer agent has been associated with the "Ethylene Glycol" pure component in Heat transfer agent properties dialog for “Glycol”.. A unit purchase cost of $1,000/MT (Cf = $1,000/MT) was also specified for the "Ethylene Glycol" pure component through the corresponding Pure Component Properties dialog. As you can see in Heat transfer agent properties dialog for “Glycol”., the "Material/Agent Used" ratio has been set to 0.05 to indicate that 5% of the total amount of heat transfer agent used in the chiller is fresh material (mf/mt = 0.05). Then, Cf’ can be calculated as follows: Cf' = mf/mt * Cf = 0.05 * $1,000/MT = $50/MT. This is the "Cost" shown in Heat transfer agent properties dialog for “Glycol”.. If we assume that another $10/MT is needed to bring the glycol to the specified supply temperature of -10°C (Ce = $10/MT), then the total unit cost of the heat transfer agent is: Ct = Cf' + Ce = $60/MT.
Heat transfer agent properties dialog for “Glycol”.
This is the value that must be entered for the mass-based unit cost of the "Glycol" heat transfer agent in this example.
As prices of utilities tend to fluctuate in time, if your company regularly updates values in the ‘SuperPro (User)’ database, you may decide to bring all prices in your SuperPro Designer model up-to-date. This can be easily done by invoking the Update Resource Prices from SuperPro (User) DB Dialog (select } from the main menu of the application).
Credit Price of a Heating Transfer Agent
If the user manages to find a cooling load in the process that is thermodynamically compatible with the heating required to regenerate a heat transfer agent we can receive credit for the equivalent amount of that agent at a credit rate equal to the ‘Agent Credit Price’ set at the corresponding box at the bottom right of the agent’s properties dialog (see Heat transfer agent properties dialog for “Hot Water”.). For the heating agent shown in Heat transfer agent properties dialog for “Hot Water”. (‘Hot Water’) the user must find a heating ‘donor’ that can provide heat to raise a spent amount of ‘Hot Water’ from its return temperature (30°C) to its supply temperature (40°C). In other words, the user must find an operation that requires cooling load (e.g. a distillation column’s condenser load) with an start temperature higher than 40°C and a target (exit) temperature above 30°C. Such heat recovery opportunities can be found by invoking the Energy Recovery Opportunities Dialog. Once such a potential heat donor is located from the dialog, then from the next screen (Recovered Energy Matches Dialog) the option “Match with Spent Heating Agent” should be chosen, and from the list of
Heat transfer agent properties dialog for “Hot Water”.
displayed heat transfer agents, ‘Hot Water’ should be selected. If the process currently is using ‘Hot Water’ as a heating agent (anywhere), the equivalent amount that can be regenerated from the matching cooling load will be subtracted, thereby producing savings or reduction of the of the annual operating cost (AOC), see Savings. If the process is not using as much ‘Hot Water’ as can be regenerated from the recovered amount of heat, or perhaps, it is not using ‘Hot Water’ at all, then the remaining amount of agent will be converted into credit (at a rate matching the ‘Credit Price’ specified in the agent’s property page). This credit will be added to the income generated by the process (see Credits) thereby improving the economic viability of the process. It’s worth mentioning that after the above match is made, the economics of the process will be improved not only from the savings or credit for ‘Hot Water’ but also from the elimination of the cooling agent that is now no longer needed on the cooling side (in our case, agent used for the cooling load in the distillation column’s condenser). Elimination of the condenser’s cooling agent will be reflected as savings or reduction of the AOC (see Savings).
