ENVIRONMENTAL ENGINEERING:ESTIMATING PLANT-WIDE EMISSIONS

By -
ESTIMATING PLANT-WIDE EMISSIONS
Overview

A part of the overall air pollution requirements is an annual emissions inventory to be submitted to the state in which the source resides. This inventory identifies and quantifies all significant atmos- pheric discharges from the respective industrial plant. Most states now have this inventory in elec- tronic form and require submission electronically. The Indiana Department of Environmental Management uses a commercial package called i-STEPS, which is an automated tool for storing, reporting, and managing air emissions data. i-STEPS facilitates data compilation for pollution man- agement and reporting emissions data to government agencies.*

Estimating Methods
Mass Balance

From an engineering viewpoint, the most direct way to estimate pollution emissions from an industrial plant is by mass balance. The concept is ‘‘mass in = mass out’’—that is, everything the purchasing department buys and is delivered to the plant must somehow leave the plant, whether within the manufactured product; as solid waste to a landfill; as air emissions either through a stack or vent; or as liquid waste either to an on-site treatment plant or to the sewer and the municipal wastewater treatment plant.

* i-STEPs Environmental Software is available from Pacific Environmental Services, Inc., 5001 South Miami Boul- evard; Suite 300, P.O. Box 12077, Research Triangle Park, NC 27709-2077, www.i-steps.com.

The mass balance approach, however, does not necessarily yield exceptional accuracy. Accuracy is a function of understanding the way in which a particular feed stock or raw material is used and how much of it is released to the atmosphere or perhaps transformed in the process. The mass balance approach would probably be used if measured parameters were not available, such as stack emission data and wastewater effluent data.

An example where a mass balance approach would yield inaccurate emissions to the atmosphere would be an industrial resin coating line. This process uses an organic carrier solvent, such as ethanol, which is volatized from the resin solids in a drying oven. The vapors (volatile organic compounds [VOCs]) are then incinerated. The ethanol can be transformed into other organic compounds in the incinerator. The total mass of applied carrier solvent (ethanol) would not be accounted for in the incinerator exhaust gas stream due to its transformation into other organic compounds.

Emission Factors

Emission factors are unique to the air pollution field. They are usually based on stack emission test data for a specific process and are presented as a ratio of two flow rates. The numerator is the mass flow rate of the air pollutant parameter and the denominator is the flow rate of the process or manufactured product. In the spraypainting of automobiles, for example, the carrier solvent in the paint (VOC) is released to the atmosphere as the paint is dried in an oven. A stack test quantifies the amount of paint VOC released during the painting of some quantity of autos. The resulting VOC emission factor would be lb-VOC / hr divided by # of autos / hr painted. Note that the hour (hr) unit cancels and the emission factor is expressed as lb-VOC / # autos.

The U.S. Environmental Protection Agency publishes AP-42, a well-known compilation of air pollutant emission factors that contains emission factors for many industrial process and manufac- turing operations (EPA AP-42 1995).

To illustrate the use of an emission factor, let us turn to the fish-canning industry. From AP-42, section 9.13.1-7 and Table 3, entitled ‘‘Uncontrolled Emission Factors for Fish Canning and By- product Manufacture,’’ emission factors are shown for particulate emissions, trimethylamine (fish odor), and hydrogen sulfide (rotten egg odor). Emissions from the fish scrap cookers for both fresh fish and stale fish are shown. Notice that the particulate emissions are negligible for the cookers. Trimethylamine (fish odor) has an emission factor of 0.3 lb-trimethylamine / ton of fresh fish cooked. If we are cooking 5 tons of fresh fish / hr, then the uncontrolled fish odor emission to the atmosphere is 0.3 lb-trimethylamine / ton of fresh fish cooked X 5 tons of fresh fish / hr = 1.5 lb-trimethylamine/ hr. Since the chemical responsible for typical fish odor is trimethylamine, 1.5 lb / hr will certainly be noticed by residents’ noses downwind of the plant.

For hydrogen sulfide (H2S, rotten egg odor), the uncontrolled atmospheric emission factor is 0.01 lb-H2S / ton of fresh fish cooked. If we are cooking 5 tons of fresh fish / hr, then the uncontrolled H2S odor to the atmosphere is 0.01 lb-H2S / ton cooked fresh fish X 5 tons cooked fresh fish / hr = 0.05 lb-H2S / hr. It is interesting to note that if the cooking fish is stale, not fresh, the trimethylamine emission is over 10 times higher. Similarly, for the hydrogen sulfide, if the fish is stale, the hydrogen sulfide emission is 20 times greater. With the concept of the emission factor, uncontrolled emissions

SNAG-0335

from fish cookers can be estimated without costly measurements. The expected accuracy of the estimate is alluded to at the top of the table as having an emission factor rating of C. This means that on a scale of A to E, with A being the relative best estimate, the C rating is mediocre. It is important to refer to the references associated with each emission factor so a value judgment can be made when using the factor.

Comments

Post a Comment

Popular posts from this blog

MATERIAL-HANDLING SYSTEMS:STORAGE SYSTEMS

By -
Image
STORAGE SYSTEMS Various types of racks have been developed to store loads of different sizes and shapes. One of the simplest storage systems is block stacking, where loads (which may or may not be palletized) are simply stacked on top each other with no separate support structure. While block stacking is inex pensive and provides dense storage (i.e., little or no space is lost due to air between the loads), its use is limited in practice because only certain types of loads (such as appliances or furniture packed properly in cartons) can be stacked without crushing / damaging the loads at the bottom and access to individual loads (i.e., load selectivity) is very limited. In fact, loads must be removed from a stack, starting with the load at the top. This leads to last-in-first-out (LIFO) stock rotation, which is not desirable for many storage systems. A fundamental trade-off that exists in storage systems design is that between storage density (how well the cubic volume is utilized) ...
Read more

NETWORK OPTIMIZATION MODELS:THE MINIMUM SPANNING TREE PROBLEM

By -
Image
THE MINIMUM SPANNING TREE PROBLEM The minimum spanning tree problem bears some similarities to the main version of the shortest-path problem presented in the preceding section. In both cases, an undi r ecte d and connected network is being considered, where the given information includes some mea- sure of the positive length (distance, cost, time, etc.) associated with each link. Both problems also involve choosing a set of links that have the shortest total length among all sets of links that satisfy a certain property. For the shortest-path problem, this property is that the chosen links must provide a path between the origin and the destination. For the minimum spanning tree problem, the required property is that the chosen links must provide a path between ea c h pair of nodes. The minimum spanning tree problem can be summarized as follows: 1. You are given the nodes of a network but not the links. Instead, you are given the po- tential links and the positive length for each ...
Read more

DUALITY THEORY:THE ESSENCE OF DUALITY THEORY

By -
Image
THE ESSENCE OF DUALITY THEORY Given our standard form for the primal problem at the left (perhaps after conversion from another form), its dual problem has the form shown to the right. Thus, with the primal problem in maximizatio n form, the dual problem is in minimization form instead. Furthermore, the dual problem uses exactly the same pa r amete r s as the primal problem, but in different locations, as summarized below. 1. The coefficients in the objective function of the primal problem are the right-hand sides of the functional constraints in the dual problem. 2. The right-hand sides of the functional constraints in the primal problem are the coef- ficients in the objective function of the dual problem. 3. The coefficients of a variable in the functional constraints of the primal problem are the coefficients in a functional constraint of the dual problem. To highlight the comparison, now look at these same two problems in matrix notation (as introduced at the beginn...
Read more