Process Flow Diagram, it's Types and it's Objectives

Process Flow Diagram

·       A diagram representing the entire process sequentially by means of equipment symbols and lines indicating all equipment and flow directions is called as “Process Flow Diagram ”.

·       The Process Engineering Department furnishes the piping analyst a Process Flow Diagram .

·       The Process Flow Diagram shows how the various items of process equipments are interconnected such as columns , heat exchanger , blowers and pumps, etc.

·       The Process Flow Diagram also indicate chemical & physical properties such as :-

         i) Flow rates, viscosity

        ii) Specific gravity, Bulk density

       iii) Molecular weights

       iv) General flowing materials

        v) Expansion factors

       vi) Temperatures

      vii) Pressures

·       It also shows the process requirements for fixed points in the process.

Objectives of PFDs :-

·       To indicate pictorially the inter-relationship among various unit operations and process units.

·       To provide material balance at all major steps.

·       To provide energy balance in the form of specific heat, temperature and state of material.(liquid,vapour or gas).

General Considerations while constructing PFDs :-

·       It is desirable to show all the equipments in their relative positions, for eg., pumps and compressors are at ground level.

·       Main process streams are always in bold, e.g., raw material to finished products.

·       The streams are numbered within a diamond.

·       Equipments are numbered generally based on function or area .

·       PFDs are also drawn for utilities , effluent treatment process.

·       While continuing PFD on other drawing sheet, one must indicate interconnection between various streams.

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Piping & Instrumentation Diagram(P&ID) , it's Types and it's Objectives

Piping & Instrumentation Diagram

·       Piping & Instrumentation Diagram are commonly called as P&IDs, and are used to guide detailed design and construction of process plants.

·       The mechanical aspects of each and every equipment are depicted in P&IDs to enable the construction personnel to construct the plant and to enable the maintainance personnel to maintain the same in order to sustain production as per the desired schedule.

·       P&IDs are constructed with the help of PFDs.

Objectives of P&IDs :-

·       To make pictorial presentation resembling the real plant as close as possible to all equipment, piping, instruments,etc.

·       To assist Plant Construction Engineers to construct the plant.

·       To assist commissioning engineers for mechanical commissioning.

·       To identify all piping with or without insulation.

·       P&IDs are also a principal form of communication between those who are designing the plant and those who are going to own and operate it .

·       To ensure success and satisfaction, it is important that P&IDs be complete and clear.

·       A P&ID is a pictorial representation of a plant , which shows all the  equipment, including installed spares plus the associated piping ,valving , insulation and instrumentation.

·       There are separate P&IDs for different systems, and the plant may be broken into sections, since a single drawing cannot typically describe an entire plant.

·       Designs are likely to change as the project moves ahead , so the P&IDs go through several revisions by the time the plant is actually built.

·       There are standard symbols for most items in P&IDs .

Types of P&IDs :-

There are 3 basic types of Piping & Instrumentation Diagrams :-

(1) System P&IDs

(2) Distribution P&IDs

(3) Auxillary System P&IDs

System P&IDs :- It shows production, utility and pollution control process. In this, there are 3 types of P&IDs , which are as follows :-

    (i)                          Process P&IDs :- These drawings are for the actual manufacturing process. Reaction, Purification, material handling, separation and other unit operations from the process form the Process Flow Diagram. Process P&IDs show all the process equipment , piping and controls. The main process flow is left to right.

   (ii)                       Utility-Generation P&IDs :- These drawings show utility systems such as boiler , cooling towers , fluid heaters , brine coolers and air compressors, but they do not typically show how these utilities are distributed through the plant.

   (iii)                    Environmental P&IDs :- These P&IDs are for pollution control processes such as scrubbing and waste-water treatment.They follow the same format as Process P&IDs.

Distribution P&IDs :- These show how utilities , chemicals and other non-process streams are distributed through the plant. These drawings include all headers and sub-headers , laid out to approximate their actual arrangement. Vents and other relief systems also fall under this category.

Auxillary  System P&IDs :-  These show compressor, lubrication and cooling systems, hydraulic systems, pump scals and other auxiliaries related to major equipment.

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HEAT TRANSFER COEFFICIENTS FOR FORCED CONVECTION IN TUBES

HEAT TRANSFER COEFFICIENTS FOR FORCED CONVECTION IN TUBES

For a tube of radius R and length L , the total heat flow into the fluid at the pipe wall is :-

                           ………..Eq 1

This statement is being valid for laminar or turbulent flow. The +ve sign appears here because the heat is added to the system in the-r direction.

Solving equation 1  for h1 ,we get

              ……Eq 2

Next we introduce the dimensionless quantities as, 

We know,

Multiplying Equation 2 by D/K ,we get,

……Eq 3

Boundary Conditions :

 

The dimensionless time-smoothened temperature will have the following dependence:-

                                                  ……Eq 9

Substitution of this relation in to equation 3 gives :-

In most practical situations, the viscous dissipation effects are small so that the Brinkman group can be neglected. 

Hence Dimensional analysis has told us that for forced convection in tubes with constant wall temperature,The Heat Trasfer Coefficient  h1  may be correlated in terms of dimensionless group Nu1 . 

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