6.0 Control Equipment Cost

Economics are always an issue in engineering practice. In a typical project, we incur expenses and acquire revenues over time, and we face the challenge of determining the best project decisions, where best means achieving the highest net profit.  Fortunately, methods for economic analysis are readily available.  These methods consider the time-value of money and provide appropriate measures of profitability, such as net present value (NPV).  The methods for economic analysis are presented in many excellent textbooks, for example, Blank and Tarquin (2002).

Engineers are responsible for estimating the benefits and costs of a project.  The benefits accrue from improved operation that improves product quality, increases reactor selectivity and separator recovery, increases production rates, reduces fuel consumption, and reduces undesirable effluents.  The approaches and calculations for determining the benefits depend upon the specific project.  General approaches and example data and calculations are available in, among others, Marlin et. al. (1987) and Shunta (1995).

 

            This section presents some useful information for estimating the cost of control equipment.  We must recognize the cost includes the following components.

 

·                     Purchase

·                     Transportation from supplier to user

·                     Installation and documentation

·                     Calibration

·                     Maintenance over the equipment lifetime

 

Some typical purchase costs are given in this section.  Transportation cost clearly depends on the particular item and supplier.  Installation includes the wiring, power, and programming any associated computing equipment.  Calibration includes checking that the proper signal is connected to the desired computing element and ensuring that standard signals evoke the desired result, e.g., a temperature at the sensor provides the correct reading for display, alarm and control.  Maintenance includes the cost of personnel and spare parts.

 

            Typical purchase costs are given in Tables 6.1 to 6.3 at the end of this section.  Most of this data has been provided by Liptak (2003; Liptak, 1999), who provides much valuable detail about each item.  Proper cost estimation requires that the equipment matches the process requirements, which requires careful evaluation of equipment performance.  Therefore, reference to Liptak (2003) and to suppliers’ data is strongly recommended when performing cost estimations.  However, the following typical data can be helpful for educational purposes and for quickly screening many potential projects.

 

            In addition, we must recall that prices are a commercial decision negotiated between purchasers and suppliers.  We expect that an order of many components will have a lower unit price than an order of one or a few components.  The data below is typical for unit purchases.

 

            Finally, engineers use “quick and dirty” approximate estimates when initially evaluating many projects.  These methods are not very accurate, typically having uncertainty of ±30% or more.  An example that is often needed is the cost of all instrumentation, including installation, for a plant construction project.  Estimates are available (e.g., Perry’s Handbook, 1997); however, the technology and costs have been changing rapidly, especially since the introduction of fieldbus digital communication.  Therefore, caution must be used when applying correlations based on old technology, often from the 1960’s.

 

 

Table 6.1 Sensors (conventional technology with transmitter, additional cost for “smart” features to be compatible with fieldbus technology)

Process variable	Cost (US$ in 2003)	Comments
Flow - orifice	500-3500	Flange connections, 2-12 in pipe
Flow - pitot and similar	1000-2000	Calibration costs extra
Flow - mass	1500-7000	1 in. pipe, cost depends strongly on sensor technology
Flow - positive displacement	3000-5000	1500 SCMH
Flow - turbine	3000	2-3 in. pipe, cost depends strongly on pipe size
Flow - venture/nozzle	500-1000	6 in. pipe, costs vary depending on sensor type and materials of construction
Temperature - thermocouple	200	Cost includes thermal well.  With transmitter could cost up to $2000
Temperature - RTD	100-250	Cost includes thermal well.  With transmitter could cost up to $2000
Temperature - thermister	See RTD
Temperature - optical pyrometer	500-5500	Thermal imaging much more expensive
Temperature - bimetalic	65	For local display only
Pressure - bourdon	300	Local indication
Pressure - electronic	1000-4000	Many technologies (See Liptak, 2003)
Level - pressure difference	1500	Local indicators few hundred dollars
Level - float	2000-5000	Switch or local indicator lower cost
Level - displacement	2500
Level - Laser	4000-6000
Level - Radar	1500-5000
Level - Ultransonic	650-2500
Analyzer - sampling system	3500-7000	Single sample stream
Analyzer - installation	--	Varies depending upon the location, safety requirements, and analyzer technology
Analyzer	--	Must determine the cost for each analyzer type individually

 

 

Table 6.2 Controllers

Controller	Cost (US$ in 2003)	Comments
Temperature - regulators	400-1000
Pressure - regulators	150-3000	Depends on pipe size and technology
Flow - regulator	250-1750
Controller, electronic or digital	500-6000	Depends on flexibility in algorithms and number of controllers in single digital controller
Controller - pneumatic	1000-2500
Distributed Digital Control System	--	See Liptak (1999) for a sample cost estimate for an integrated system

 

Table 6.3 Final elements

Final Element	Cost * (US$ in 2003)	Comments
Actuator	--	Cost included in valve cost
Ball valve body	2000	4 in piping
Butterfly body	2000	²
Globe valve body	3000	²
Diaphragm valve body	300-600	²
Accessories - positioner	600	²
Accessories - handwheel	500	Maximum cost
Accessories - limit switch indicator	50-150

*  Note that all valve costs depend on the pipe size, materials of construction, etc.  See Liptak (1999) and other resources for correlations of cost vs. pipe size and materials of construction.