Stream Calculator Unit Operation - Technical Information

The stream calculator is a flexible unit which allows you to blend any number of feed streams and produce products with defined composition and thermal condition. You may split the blended feed into two product streams and/or create a pseudoproduct stream. A feed to the unit is not required in order to create a pseudoproduct.

One of the main advantages of the unit is that you can use the Define system to create a stream with a composition determined from results calculated in other unit operations during the flowsheet convergence. For example, you could calculate the required purge or make-up stream in order to converge a difficult recycle calculation. See Stream Calculator Parameters Available for Cross-Referencing for more details.

Calculation Method

The Stream Calculator operation is in three distinct sections:

Feed blending: blend feed streams in any proportions. Scale factors (positive or negative) may be applied to all feeds in the Feed Scaling Window in order to create a mixed feed with the desired composition. If scale factors other than 1.0 are used, the unit will not material balance.

Stream Splitting: split the feed(s) into two product streams which have different compositions. For each component, you define how much goes into one product in the Product Specifications Window and the remainder goes into the other. The thermal condition specifications may optionally be entered in the Overhead Product Conditions Window and the Bottoms Product Conditions Window. Pressure defaults to the lowest feed pressure. If no temperature specification is supplied for either product, the product temperatures are set equal at a value to meet the enthalpy balance, including any duty value entered on the Stream Calculator Main Window. If one temperature is supplied, the other temperature is calculated to meet the enthalpy balance. If both temperatures are given, duty is calculated.

Stream Creation: create a pseudoproduct from the unit. If the unit has no feeds, you must define the component rates in the pseudoproduct in the Pseudoproduct Specifications Window. If the unit has a feed, you may specify the product in terms of the feed composition. If a pseudoproduct is created, the unit never material balances. If there is no feed to the unit, you must define the pseudoproduct thermal condition in the Pseudoproduct Conditions Window. If there is a feed, the temperature and pressure specifications are optional. The pressure defaults to lowest feed pressure and the temperature is calculated to satisfy the enthalpy balance. If a duty was supplied, it will be used only for the stream splitting enthalpy balance. Duty is not used for the pseudoproduct enthalpy balance.

You may split the feeds and create a pseudoproduct from the same stream calculator unit. In this case, the pseudoproduct is not included in the stream splitting material balance.

Feeds and Products

The stream calculator may have any number of feed streams which are blended in the defined proportions. If no feed is defined, then a pseudoproduct must be specified for stream creation mode.

Each product may have up to four process product streams, with each stream being of a different phase. The possible phases are: vapor; liquid; decanted water (or second liquid phase); mixed (a mixture of liquid and vapor); and solids. The phases are defined on the Product Phases Window.