Electrostatic Stimulation of Fabric Filtration

The concept of electrostatic stimulation of fabric filtration (ESFF) has been investigated at pilot scale. The pilot unit consisted of a conventional baghouse in parallel with an ESFF baghouse, allowing direct comparison. All results reported in this paper are for pulse-cleaned bags in which the electric field was maintained parallel to the fabric surface. The performance of the ESFF baghouse has been superior to the parallel conventional baghouse by several measures. The ESFF baghouse demonstrated: (1) a reduced rate of pressure drop increase during a filtration cycle, (2) lower residual pressure drop, (3) stable operation at higher face velocities, and (4) improved particle removal efficiency. These benefits can be obtained with only minor modifications to conventional pulse-jet hardware and at low electrical power consumption. The indicated ability to operate at increased face velocities with only modest expenditure for electrical hardware leads to very favorable economic projections.     

Sensitivity Studies of the Effects of Model Formulation on the Evaluation of Control Strategies for Photochemical Air Pollution Formation in the United Kingdom

In the OZIPP (ozone isopleth plotting package, developed by United States Environmental Protection Agency) a number of model specific assumptions with respect to chemical and physical processes are made. These assumptions are introduced into an alternative model developed at AERE Harwell, United Kingdom, in which a detailed chemistry and mixture of organic emissions is included. The impact on the AERE Harwell model results of the assumptions made in OZIPP of omitting ground removal of ozone (O₃) and peroxyacetylnitrate (PAN) and of employing an incomplete PAN chemistry and adopting a reaction rate coefficient of the key reaction NO + HO₂ → NO₂ + OH which is a factor 10 lower than the accepted value, are discussed. The composition of the organic emissions is an important model parameter, and it is shown how grouping of nonmethane hydrocarbon (NMHC) emissions into a small group of NMHC thought to be representative, often implies that O₃ and other pollutants are overestimated. The O₃ isopleth diagram for London constructed using the AERE Harwell model gives a somewhat different picture from that obtained with OZIPP. OZIPP in general predicts that NO_x control or combined hydrocarbon(HC) and NO_x control is efficient with respect to O₃ reduction whilst the AERE Harwell model predicts that HC control alone usually is more efficient than combined HC and NO_x control. Furthermore NO_x control alone may often increase the O₃ burden downwind in the AERE Harwell model.     

Change in Pulmonary Function in Children Associated with Air Pollution Episodes

Pulmonary function of approximately 200 school children in Steubenville, OH was measured before and immediately following air pollution alerts in the fall of 1978 and 1979. TSP concentrations exceeded the National Primary Ambient Air Quality 24 h standards in 1978. SO₂ exceeded the standard in 1979. The children were then reexamined in three weekly visits following each alert. Estimated mean Forced Vital Capacity (FVC) was approximately 2% lower following each alert, although the lowest means were observed one to two weeks after the episodes. Forced Expired Volume in 0.75 sec (FEV_0.75) did not change during the 1978 study, but was 4% lower immediately following the 1979 alert. The children were measured again in five weekly examinations in the spring and fall of 1980. Air pollution levels did not exceed the standards on either occasion. In the spring of 1980, estimated mean FVC and FEV_0.75 showed a decline similar to that observed following the alerts in 1978 and 1979. In the fall of 1980, there were no significant differences in the estimated mean FVC or FEV_0.75 between the examinations. A total of 335 children were tested in the four studies, including 194 who participated in more than one study. The evidence for each child from all the studies was combined in a regression analysis of pulmonary function on TSP and SO₂ average concentrations in the previous 24 h. The distribution of the individual regression coefficients was centered significantly below zero, implying a decrease in pulmonary function with increasing TSP and SO₂ concentrations. The magnitude of the median change was less than 1% of the mean FVC and FEV_0.75 over the range of TSP and SO₂ concentrations observed.     

Evaluation of Selected Gaseous Halocarbons for Use in source Test Performance Audits

A repository of 38 gaseous organic compounds in compressed gas cylinders has been established by EPA. This repository was established to provide standards for source test performance audits, that is, quantitative quality assurance tests. Among these compounds are ten halogenated organic species, which are the focus of this paper.

Stability studies of all ten compounds have been performed to determine the feasibility of using them as performance audit standards. Results indicate that all of the halocarbons tested are adequately stable to be used as reliable audit standards.

Subsequent to completion of stability studies, four of the ten halocarbons were used in source test performance audits. Results are available at this time for two of the four compounds; the results show agreement within 10% of the concentrations previously established by Research Triangle Institute.     

Improving Baghouse Performance at the Monticello Generating Station

At the Monticello station, operated by the Texas Utilities Generating Company, lignite coal obtained locally in Titus and Hopkins Counties fuels each of the three units. Units 1 and 2 are identical 575-MW Combustion Engineering (CE) boilers, each of which discharges its effluent to a 36- compartment shake/deflate cleaned baghouse paralleled with four electrostatic precipitators (ESP). Unit 3 is a larger boiler and is followed by an ESP and a scrubber. The Unit 1 and 2 baghouses were designed to clean 80 percent of the flue gas. Since startup, these baghouses have regularly experienced flange-to-flange pressure drops in excess of 10 in. H₂O, with large opacity spikes caused by ash bleeding through the bags after compartment cleanings. Because of higher-than-expected pressure drop, the baghouses receive only about 45-50 percent of the flue gas. Analysis has shown the Monticello lignite ash significantly differs from most other coal ashes. Testing has shown that the Monticello ash is not filtered effectively by many "standard" bag materials. However, this testing indicates that there are fabrics that show promise of eliminating the ash bleedthrough with little pressure drop penalty. Testing has also shown that injection of low concentrations (10-15 ppm) of ammonia (NH₃) into the flue gas significantly decreases ash bleedthrough, so that with NH₃ injection "standard" bag materials may perform adequately. Currently, fullcompartment testing of four fabrics, with and without NH₃ injection, is under way at the Unit 1 baghouse. The research conducted at the Monticello station is reviewed in this paper and the encouraging results from the full-compartment tests are presented.