This tab is part of the dialog that presents the properties of a heat transfer agent registered for use in the process. It allows you to edit the main properties and the cost data of the agent.
From this tab you may choose to make the heat transfer agent storable or not. Making it storable will allow you to specify inventory data and generate inventory charts.
From here you can set the supply and return temperatures of the agent, as well as the mass-to-energy factor.
|
|
The property mass-to-energy-factor represents a number that the application uses to convert heating (or cooling) energy flows (in kcal/h) to mass flows of the corresponding agent (kg/h). For agents that transfer energy as sensible heat, the mass-to-energy factor represents the heat capacity of the material utilized as an agent times the allowable agent temperature change (set by the utility plant that supplies the agent). For agents that transfer heat by condensation (or vaporization) the mass-to-energy-factor represents the heat of vaporization (at the contact temperature) of the agent (see Mass-To-Energy Estimation Dialog). For some agents, the factor may be a combination of both: for example, suppose the process draws a superheated steam (5 bar) at 160° C and it is expected to return it as a sub-cooled water at 145°C (boiling point of steam at 5 bar is 151.85°C). |
You can use this section of the interface to associate the agent’s composition material with an ingredient registered in the process. In that case the button that allows you to estimate the mass-to-energy-factor (the button with the calculator) gets activated and you can click on it to access the Mass-To-Energy Estimation Dialog.
Once the Heat Transfer Agent is associated with a material, the consumption of this material as a Heat Transfer Agent is also included in the material consumption chart. See also Material Selection for Consumption Chart.
|
|
It is important to understand that the consumption factor specified there, is supposed to represent the make-up amount of material needed to be supplied by the utility plant during the heat transfer agent’s regeneration process; it does NOT represent the entire amount of agent being regenerated. For a more detailed explanation of this cost and to see how the material and energy cost components together make up the final (total) cost of a heat transfer agent, see The life cycle and unit cost of a heat transfer agent. |
Consumption Basis
This option defines whether the consumption of a the agent will be displayed (in charts as well as in reports) on a mass-basis or a volume-basis. If the user has chosen ‘volume-basis’ then the program must convert the amount of agent calculated in mass (based on the heat-to-mass factor) to volume and therefore a heat transfer agent density is needed. If there’s a material associated with the heat transfer agent, the program will offer to estimate the density based on the density value of that material using a user-defined value for the agent’s density.
These controls allow you to set the agent’s unit cost either on a mass (or volume) basis or on an energy basis. The mass-to-energy factor is used to convert between the two values.
Note that the agent’s unit cost is supposed to represent the cost of using the agent, rather than the unit purchase cost (the same way that the annual heat transfer agent demand shown on the List of Heat Transfer Agents Currently in Use dialog is supposed to represent the annual amount of heat transfer agent used by the flowsheet’s processes, rather than the amount of heat transfer agent that you need to buy every year). For example, consider a Cooling unit procedure that uses glycol as the heat transfer agent. The utility plant is supposed to supply the unit procedure with 100 MT/yr of glycol at a supply temperature of -10°C, and 95 MT/yr of glycol are supposed to return to the utility plant at a return temperature of 0°C (5 MT/yr of glycol are somehow lost in the way). In that case, the utility plant must spend money for two things:
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. If we assume that the unit purchase cost of fresh glycol is $1000/MT, then the cost of fresh glycol is $5000/yr. If we also assume that the cost of bringing glycol from the return temperature back to the supply temperature is $10/MT, then that cost is $1000/yr. Therefore, the total cost of the utility plant is $6000/yr, and the unit cost of the “Glycol” agent is $60/MT. For more details, see Unit Cost of Heat Transfer Agent.
|
|
The unit cost of the heat transfer agent is supposed to represent the cost of using the agent, not the cost of buying the agent. More specifically, it is supposed to represent the sum of two costs that the utility plant (which supplies the agent) has to spend: (a) the cost to bring the agent from the return temperature back to the supply temperature, and (b) the cost to buy fresh agent (if the returned amount is less than the supplied amount because a fraction of the agent is somehow lost during the agent regeneration process withing the utility plant). For a more detailed explanation of this cost and to see how the material and energy cost components together make up the final (total) cost of a heat transfer agent, see The life cycle and unit cost of a heat transfer agent. |
.
Spent Agent Loss in Process
Here the user can specify the percent of agent lost in the process, plus the cost of the lost heat transfer agent. This is unrelated to the make up amount of material of the heat transfer agent which is specified in the Agent’s Composition Material, and is represented as the percent of the agent required to regenerate the agent at the utility plant. The percent lost in the process is the percent of the heat transfer agent that did not return to the utility plant and may have a cost to replenish.
Agent Credit Price
Heating Agents may also have a mass- (or volume-) based or heat-based credit price. To understand how this price is used, you must understand how the application allows users to recover and reuse energy via the Energy Recovery Opportunities Dialog. Once a candidate cooling load is chosen (that is a load coming from an operation that requires cooling and therefore it can ‘donate’ its heat content), then we can choose either an appropriate heating load (at some other operation) or an appropriate heat transfer agent to be the receiver of that heat (see Energy Recovered Match Dialog). Of course the temperatures must be appropriate: the temperature where the ‘heat donor’ supplies the energy must be above the exit (or target) temperature of either the matching load or matching heat transfer agent. For instance, we could be using the cooling load at the condenser of a distillation column that happens to be operating at 101°C to revive “Hot Water” agent (it is returned at 25° and it must be raised to 40°C). If the process is already using “Hot Water” then the equivalent amount of “Hot Water” resulting from the recovered cooling load will be reduced from the Annual Operating Cost (AOC) of the process, thereby realizing savings for the process (see Savings). If the load amounts to more agent (“Hot Water”) than what the process is currently using, or perhaps the process does NOT use “Hot Water” at all, then the excess load will be converted to “Hot Water” amount that we assume can be ‘sold’ at the ‘credit price’ rate and the resulting monetary amount will be applied as ‘credit’ to the process economics (see Credits); in simple words, it will be added to the proceeds (or income) of the process (just like a side revenue stream would) thereby increasing the profitability of the process.
