II simulations within the time frame of the project. A series of 24-hour test simulations was

performed to determine which input parameters had the largest effect on CPU time. These

simulations, described below, clearly demonstrated that the number of puffs was the key

variable. They also suggested that the number of puffs must be reduced by a factor of 10 to

achieve the needed reduction in CPU time.

The number of puffs is governed by the puff release rate and the number of sources. The puff

release rate had been set at the default value of 4 puffs per hour. Although MESOPUFF II, as

originally configured, allows up to 1000 point sources, it only allows for a total of 10,000

puffs. With 1000 sources and a puff release rate of 4 per hour, the limit on the number of

puffs would be reached after 2.5 hours. With 27 sources and a puff release rate of 4 per hour,

the original configuration for the demonstration application, the puff limit would be reached

after 92 hours. In order to run MESOPUFF II in this configuration for one full month,

therefore, it would be necessary to increase the maximum number of puffs substantially. This

would require re-compiling MESOPUFF II and would increase the size of the executable

code. Since the MESOPUFF II executable, at 3.3 MB, is near the limit for use on a PC with 4

MB memory, the maximum number of puffs might be a limiting factor even if CPU time

considerations were not.

In order to reduce the number of puffs by a factor of ten and still preserve at least a portion of

the original intent of the demonstration application, the puff release rate was reduced from 4

puffs per hour to 1 puff per hour. This deviates from the Phase 1 recommendations; however,

because the output averaging interval used for the demonstration application was 3 hours

rather than 1 hour, this change was considered acceptable. The number of sources was

reduced from 27 to 18. Under these conditions, 25.8 CPU hours were required for the January

1988 simulation. Although this was a major improvement over the 27 source case, it was still

too slow to allow completion of the project on schedule. Further reductions in the puff release

rate were judged to be infeasible. Therefore, the number of sources was reduced further from

18 to 10. This reduced the CPU time to less than 12 hours for January 1988. This set of 10

sources was used for the demonstration application of MESOPUFF II.

In reducing the number of sources to be modeled, the goal was to retain as much as possible

of the total emissions mass, and reduce the number of sources by consolidation of nearby

sources rather than elimination of sources. In the condensation of the original 27 sources to

18 sources, sources within one grid cell of each other were consolidated. No sources were

eliminated. In order to reduce the number of sources to 10, however, it was necessary to

eliminate three small sources that were not located near other sources, and sources within 2-3

grid cells were consolidated. The consolidated sources were represented as point sources,

with coordinates and stack parameters obtained as an arithmetic mean of the individual

sources. The three sources eliminated, Westvaco, Chalk Pt., and Coal Dynamics, have total

emissions of 165 g/s SO and 214 g/s NO . This amounts to 5 percent of the total SO 2 x 2

emissions of the original 27 sources, and 8 percent of the total NO emissions. Table 3-2 x

shows the final set of 10 consolidated sources, the facilities that are included in each, and the

location and emission parameters

 

 

n1301 - n1302 - n1303 - n1304 - n1305 - n1306 - n1307 - n1308 - n1309 - n1310 - n1311 - n1312 - n1313 - n1314 - n1315 - n1316 - n1317 - n1318 - n1319 - n1320 - n1321 - n1322 - n1323 - n1324 - n1325 - n1326 - n1327 - n1328 - n1329 - n1330 - n1331 - n1332 - n1333 - n1334 - n1335 - n1336 - n1337 - n1338 - n1339 - n1340 - n1341 - n1342 - n1343 - n1344 - n1345 - n1346 - n13247 - n1348 - n1349 - n1350

 

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