The total capital investment (TCI) for scrubbers includes all of the initial capital costs, both
direct and indirect. Direct capital costs are the purchased equipment costs (PEC), and the costs of
installation (foundations, electrical, piping, etc.). Indirect costs are related to the installation and include engineering, construction, contractors, start-up, testing, and contingencies. The PEC is calculated based on the scrubber specifications. The direct and indirect installation costs are calculated as factors of the PEC. Table 1 provides the TCI factors for a typical scrubber.
Wet scrubber costs are dependent upon the type of scrubber selected, the required size of the
scrubber, and the materials of construction. Scrubber sizing incorporates several design parameters,
including gas velocity, liquid-to-gas ratio, and pressure drop. Gas velocity is the primary sizing factor. Increasing the gas velocity will decrease the required size and cost of a scrubber. However, pressure drop will increase with increasing gas velocity. This will also result in increased electricity consumption and, therefore, higher operating costs. Determining the optimum gas velocity involves balancing the capital and annual costs. In most cases, scrubbers are designed to operate within recommended ranges of gas velocity, liquid-to-gas ratio, and pressure drop. These ranges are provided in Table 2.
Another important scrubber parameter that affects costs is the temperature of the gas stream at
saturation once it has been cooled by the scrubber liquid. This temperature affects the volumetric
flowrate of the outlet gas and, consequently, the size of the scrubber. In addition, the saturation
temperature impacts the scrubbing liquid makeup and the wastewater flowrate. The saturation
temperature is a complex function of essentially three variables: the temperature of the inlet gas stream, the absolute humidity of the inlet gas stream, and the absolute humidity at saturation. Typically, the saturation temperature is determined graphically from a psychometric chart once these three variables are known. For this document, the sizing and costing of wet scrubbers were aided by the use of the CO$T-AIR Control Cost Spreadsheets, that employ an iterative procedure for estimating the saturation temperature.
Once a scrubber has been properly designed and sized, the costs can generally be expressed as
a function of the inlet or total gas flowrate. Cost curves are shown below for the following types of
scrubbers: venturi, impingement plate, and packed tower.
All the estimates for scrubber capital costs have been escalated to third quarter 1995 dollars.
However, the capital costs presented in this section can be escalated further to reflect more current
values through the use of the Vatavuk Air Pollution Cost Control Indexes (VAPCCI), which are
updated quarterly, available on the OAQPS Technology Transfer Network (TTN), and published
monthly in Chemical Engineering magazine. The VAPCCI updates the PEC and, since capital costs
are based only on the PEC, capital costs can be easily adjusted using the VAPCCI. To escalate
capital costs from one year (Costold) to another more recent year (Costnew), a simple proportion can be used, as follows
The VAPCCI for wet scrubbers for third quarter 1995 was 114.7.
direct and indirect. Direct capital costs are the purchased equipment costs (PEC), and the costs of
installation (foundations, electrical, piping, etc.). Indirect costs are related to the installation and include engineering, construction, contractors, start-up, testing, and contingencies. The PEC is calculated based on the scrubber specifications. The direct and indirect installation costs are calculated as factors of the PEC. Table 1 provides the TCI factors for a typical scrubber.
Table 1, Capital Cost Factors for a Typical Scrubber
Wet scrubber costs are dependent upon the type of scrubber selected, the required size of the
scrubber, and the materials of construction. Scrubber sizing incorporates several design parameters,
including gas velocity, liquid-to-gas ratio, and pressure drop. Gas velocity is the primary sizing factor. Increasing the gas velocity will decrease the required size and cost of a scrubber. However, pressure drop will increase with increasing gas velocity. This will also result in increased electricity consumption and, therefore, higher operating costs. Determining the optimum gas velocity involves balancing the capital and annual costs. In most cases, scrubbers are designed to operate within recommended ranges of gas velocity, liquid-to-gas ratio, and pressure drop. These ranges are provided in Table 2.
Table 2. Recommended Gas Velocities, Liquid/Gas Ratios,
and Pressure Drops for Particulate Wet Scrubbers
Another important scrubber parameter that affects costs is the temperature of the gas stream at
saturation once it has been cooled by the scrubber liquid. This temperature affects the volumetric
flowrate of the outlet gas and, consequently, the size of the scrubber. In addition, the saturation
temperature impacts the scrubbing liquid makeup and the wastewater flowrate. The saturation
temperature is a complex function of essentially three variables: the temperature of the inlet gas stream, the absolute humidity of the inlet gas stream, and the absolute humidity at saturation. Typically, the saturation temperature is determined graphically from a psychometric chart once these three variables are known. For this document, the sizing and costing of wet scrubbers were aided by the use of the CO$T-AIR Control Cost Spreadsheets, that employ an iterative procedure for estimating the saturation temperature.
Once a scrubber has been properly designed and sized, the costs can generally be expressed as
a function of the inlet or total gas flowrate. Cost curves are shown below for the following types of
scrubbers: venturi, impingement plate, and packed tower.
All the estimates for scrubber capital costs have been escalated to third quarter 1995 dollars.
However, the capital costs presented in this section can be escalated further to reflect more current
values through the use of the Vatavuk Air Pollution Cost Control Indexes (VAPCCI), which are
updated quarterly, available on the OAQPS Technology Transfer Network (TTN), and published
monthly in Chemical Engineering magazine. The VAPCCI updates the PEC and, since capital costs
are based only on the PEC, capital costs can be easily adjusted using the VAPCCI. To escalate
capital costs from one year (Costold) to another more recent year (Costnew), a simple proportion can be used, as follows
0 comments:
Post a Comment