9.3 EFFECT OF DEPRECIATION
9.4.1 D ESIGN D EVELOPMENT
In order to employ cost estimation and profitability analysis, it is suggested that the following process be used.
1. Select a process to develop from alternative processes.
2. Prepare the process flowsheet.
3. Optimize the process flowsheet. Generally, a process simulation software package (Aspen Plus, Aspen Hysys, etc.) is used for process optimization studies.
4. Apply process integration technologies to the process flowsheet to minimize utility costs and to minimize waste generation. This step may be included simultaneously with steps 2 and 3.
5. Calculate sizes of all equipment and estimate fixed capital cost.
6. Estimate installed cost.
7. Determine utilities usage and estimate cost.
8. Determine other costs—taxes, buildings, land, and insurance.
9. Undertake a profitability analysis.
A good list of all other costs to be considered can be found in Seider et al.4
In carrying out the design, it is recommended to set a budget for pollution control equipment. Then make as accurate a cost estimate as possible. There are four suggested approaches for arriving at a cost estimate. They are as follows:
1. Order-of-magnitude estimate (±50%): Based on bench-scale laboratory data sufficient to determine the type of equipment and its arrangement 2. Study estimate (±35%): Based on preliminary process design
3. Preliminary estimate (±20%): Based on detailed process design, including optimization
4. Definitive estimate (±10%): Based on detailed plant design with equipment drawings and vendor cost estimates
Keep in mind that the designer must maintain a satisfactory profit structure if alter- nate choices are available. The following factors will affect equipment costs:
• Company policies
• Local and federal government regulations
• Design standards
• Union contracts and agreements
• Agreements with fabricators
• Economy of scale (equipment size)
• Equipment materials of construction
• Operating pressures
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10 Introduction to Control of Gaseous Pollutants
Under the auspices of the Environmental Protection Agency (EPA)’s Center for Environmental Research Information in conjunction with the EPA Control Technology Center, a handbook for design of hazardous air pollution control equipment was published in 1986. A revised version of the handbook was published in June 1991.1 Current information is furnished through the Clean Air Technology Center. This cen- ter serves as a resource on all areas of emerging and existing air pollution prevention and control technologies and their cost. The information now may be found on the following website: http//www.usepa.gov/ttn/catc/.
There are six main processes by which a gaseous pollutant may be removed from an air stream. Table 10.1, taken from the EPA handbook,1 lists those processes with the advantages and disadvantages of using each one. The table may be used as a guide to determine which process may provide the best means of cleaning the air stream. Separation processes are used as a means of air pollution control for both particulate matter and gas. These processes essentially remove the pollutant from the carrier gas resulting in a cleaned gas stream. If the pollutant content of the cleaned stream meets the effluent emission standards, the cleaned stream can be discharged to the atmosphere. Absorption and adsorption are both diffusional separation pro- cesses that can be used to collect hazardous air pollutants. In the case of absorption, the pollutant is transferred to the solvent, which then may need further treatment, referred to as regeneration. Recovery of the solvent might be undertaken by distilla- tion or by stripping the absorbed material from the solvent. The problem of treating the waste material in the stream separated from the solvent remains. If the pollutant material has a value, adsorption may provide the means for the material to be more readily recovered. In the case of particulate matter, wet scrubbing collects the par- ticles primarily through the mechanism of inertial impaction. Gaseous contaminants such as sulfur oxide, nitrogen oxide, and hydrochloric acid, if present along with the particulates, may be collected simultaneously by absorption.
From a systems perspective, as indicated in Chapter 8, adsorption columns and adsorbers used for the removal of gaseous pollutants are classified as mass exchang- ers, since they recover the gaseous pollutant by use of direct-contact mass transfer processes. The solvents used in absorption columns and the adsorbents employed in adsorbers to remove gaseous air pollutants are collectively referred to as mass separating agents. Absorber and adsorber systems may require regeneration of their mass separating to allow the separation and recovery of the gaseous pollutant and to allow reuse of the mass separating agents. Simultaneous synthesis of a mass exchange networks of direct contact exchangers along with its respective regenera- tion system has been addressed in the literature.2 Also, from a systems perspective,
as indicated in Chapter 8, condensers used for the removal of gaseous pollutants are classified as heat-induced separators since they recover the gaseous pollutant by use of indirect-contact cooling of the gaseous stream. The coolants used in condensers to remove gaseous air pollutants are collectively referred to as energy separating agents. Condensation systems may require coolant regeneration, such as through a refrigeration cycle, if the coolant employed is a refrigerant. Mass exchangers (absorbers, adsorbers, etc.) and heat-induced separators (condensers) are considered recovery technologies because the gaseous pollutant is removed and recovered for sale or reuse. Incinerators and flares (thermal oxidation processes) are considered destructive technologies since the gaseous pollutant is eliminated. A more detailed discussion of absorption technology, adorption technology, condensation, and thermal oxidation are provided in Chapters 11 through 14, respectively.
Many organic materials may be removed by condensation, which is essentially a diffusional operation. If a suitable coolant is available and the pollutant concentra- tion is high enough, condensation can be very effective in recovering material that may be used again. For organic pollutants when the concentration is low or recover- ing the material is not desired, incineration can be used to convert the pollutant to carbon dioxide and water. For large emissions such as those that would be found in petroleum refineries, the pollutant may be flared.
TABLE 10.1
Volatile Organic Compounds Control Technologies
Device
Inlet Conc.
PPMV Efficiency (%) Advantages Disadvantages
Absorption 250 90 Especially good for
inorganic acid gasses
Limited applicability
1,000 95
5,000 98
Adsorption 200 50 Low capital investment Selective applicability
1,000 90–95 Good for solvent
recovery
Moisture and
temperature constraints
5,000 98
Condensation 500 50 Good for product or
solvent recovery
Limited applicability
10,000 95
Thermal incineration
20 95 High destruction
efficiency
No organics can be recovered
100 99 Wide applicability Capital intensive
Can recover heat energy Catalytic
incineration
50 90 High destruction
efficiency
No organics can be recovered 100 >95 Can be less expensive
than thermal incineration
Technical limitations that can poison
Flares >98 High destruction
efficiency
No organics can be recovered Large emissions only