Question

Compare Step Counting method and detailed factorial method (Hand method) in terms of calculation constraints, calculation accuracy, design details availability and cost data availability. Then determine the best method to employ in this case.

Answer 1

FACTOIRIAL METHODE

• Capital cost estimates for chemical process plants are often based on an estimate of the purchase cost of the major equipment items required for the process, the other costs being estimated as factors of the equipment cost.
• The accuracy of this type of estimate will depend on what stage the design has reached at the time the estimate is made, and on the reliability of the data available on equipment costs.

Comparasion

Detailes factorial methode

• For more accuracy, the cost factors that are compounded into the “Lang factor” are considered .where
• Lange factor capital cost and total delivered cost are ralated as;
• Cf = fL x Ce

The direct-cost items that are incurred in the construction of a plant, in addition to the cost of equipment are:

• Equipment erection, including foundations and minor structural work.
• Piping, including insulation and painting.
• Electrical, power and lighting.
• Instruments, local and control room.
• Process buildings and structures.
• Ancillary buildings, offices, laboratory buildings, workshops.
• Storages, raw materials and finished product.
• Utilities.
• Site, and site preparation.

The contribution of each of these items to the total capital cost is calculated by multiplying the total purchased equipment by an appropriate factor.

“Lang factor”, these factors are best derived from historical cost data for similar processes.

• Detailed costing is only justified if the cost data available are reliable and the design has been taken to the point where all the cost items can be identified and included.

Step counting methods

For a rapid cost estimation step counting mehode play important role.

Step counting estimating methods provide a way of making a quick. in order of :

• magnitude
• capital cost of proposed project.

The technique is based on the premise that the capital cost is determined by a number of significant processing steps in the overall process.

Factors are usually included to allow for the

• capacity and complexity of the process.
• material of construction.
• yield.
• operating pressure and temperature.

A number of workers have published correlations based on a step counting approach.

Like TALOR, WILSON

Their equation based on plant capacities under 60,000 tonne per year.

C = 150,000 N (Q/s)^0.30

and above 60,000

C = 170 N (Q/s)^0.675.

where,

C = capital cost in pounds sterling

N = Number of functional units
Q = plant capacity, tonne per year
s = reactor conversion.

THE BEST METHODE

THE STEP COUNTING METHODE GIVES

• simple correlation for plants that are predominantly liquid and/or solid phase handing processes.

NOTE;- dear aspirant i have been conclude from many of the papers you can also go on google for more info.