Reference Data

Continued..

.. efficiency needs protection from the insulating qualities of the air entrained in the system. This can only be done effectively and economically through the mechanical deaeration process known as a deaerator. Chemical treatment of boiler feedwater as the sole method for Oxygen removal is expensive and promotes increased boiler blowdown, which increases make up, which requires more O2 reagent chemicals, which increases boiler blowdown, and creates an expensive, ongoing cycle of chemical waste and heat loss.

Deaerators are the balance point of the modern steam / condensate system, particularly for process applications (although not excluded from HVAC systems). They provide the mechanical deaeration of the boiler feedwater, a means to elevate the feedwater temperature prior to pumping that water into the boiler, and as a heat sink and collection point for condensate returns. In spite of the tendency of the many "total boiler room system" vendors to offer only one or two types of deaerators ("one size fits all!"), there are actually a number of different types of deaerators. The distinctive deaerator types achieving .005 CC/L (7 PPM) deaeration performance are:
Pressurized: 2-Stage Spray, 2-Stage Spray-Tray, 3-Stage Spray-Tray, Counter Flow & Parallel Flow Tray, Packed Column and Constant Recycle Type.
Atmospheric: 2-Stage Gravity Flow and Constant Recycle Type.
Each design has its best application, and its most economical application point. Each steam / condensate system will only work properly long term with the right deaerator. The "one size fits all" vendors are those without ongoing research and development programs, and are typically attempting to pound the proverbial square peg into a round hole. Those are the systems often replaced after 5-10 years of operation.

A careful analysis of the steam / condensate system characteristics, the process needs, and the operational criteria for the facility needs to be accomplished before any deaerator design or variations thereof is applied. The misapplication of this equipment in this system is one of the most frequent and expensive problems facing industrial process and large institutional (HVAC) boiler room owners today.

9) Efficiency:
There is much give and take about boiler passes, types of efficiencies, and the like. Often, a decision as to the vendor and type of equipment to buy is based on a boiler manufacturers published efficiency. Correct or not, these published efficiencies provide a comfort level to the purchaser, and cannot be discounted in the equipment consideration process. But, unlike the Chiller industry, there is no industry embraced standard method for determining the efficiency of a standard cataloged packaged boiler. There are the complex, but common sense guidelines of the ASME PTC 4.1 "Short Form" Power Test Code, but with all its variables, it is seldom applied as a published rating method. So what do you believe? Some manufacturers estimate "radiation & convection" losses from the boiler shell at a still air condition, while others assume there will be 2-3 FT/SEC air flow from the from the boiler room ventilation system (it makes a big difference). Some manufacturers guarantee efficiencies with money, while others recognize that you can make a boiler-burner unit achieve about anything at start up to satisfy a guarantee - but will you leave it exactly that way for normal and reliable operation?

The truth is, whether the boiler design is a 2-Pass "Dryback" Boiler with turbulators, or a 4-Pass "Dryback" Boiler, or 3-Pass "Wetback" Boiler, given the same application conditions, the efficiencies should be the same. For the skeptics, it is suggested that all of the criteria surrounding a specific boiler application be established (altitude, feedwater temperature, ambient air temperature and air flow velocity across the boiler surfaces, operational range, operating pressure, fuel values, etc.) and ask the different boiler manufacturers to produce a guaranteed calculated efficiency based on that criteria. You will be surprised to find the difference so small that is likely attributed to who rounds which number what way.

So, given that the much hyped efficiency difference is generally a wash - what makes a boiler that costs less to own year in and year out? That has to do with boiler design criteria and service, and will be addressed in the "Technical Talk" of this web site over time.

10) Saturated Steam Temperature for Various Pressures:

Gauge Pressure PSIG	Temperature ° F	Gauge Pressure PSIG	Temperature ° F
0 1 2 3 4 5	212 216 219 222 225 227	42 43 44 45 46 47	289 291 292 293 294 295
6 7 8 9 10	230 233 235 237 240	48 49 50 52 54	296 297 298 300 302
11 12 13 14 15	242 244 246 248 250	56 58 60 62 64	304 306 308 309 311
16 17 18 19 20	252 254 255 257 259	66 68 70 72 74	313 315 316 318 319
21 22 23 24 25	260 262 264 265 267	76 78 80 82 84	321 323 324 326 327
26 27 28 29 30	269 270 272 273 274	86 88 90 92 94	329 330 331 333 334
31 32 33 34 35	276 277 278 280 281	96 98 100 102 104	335 337 338 339 341
36 37 38 39 40 41	282 284 285 286 287 288	106 108 110 112 114 116	342 343 344 346 347 348

Gauge Pressure PSIG	Temperature ° F
118 120 122 124 126 128	349 350 351 352 354 355
130 135 140 145 150	356 358 361 364 366
155 160 165 170 175	368 371 373 375 378
180 185 190 195 200	380 382 384 386 388
205 210 215 220 225	390 392 394 396 397
230 235 240 245 250	399 401 403 404 406
255 260 265 270 275	408 409 411 413 414
280 285 290 295 300 400	416 417 419 421 422 448

Absolute Pressure = above gauge pressure, plus the atmospheric pressure (14.7 PSIG @ sea level).

For all inquiries about support and services send questions to mhallford@wcrouse.com or jhodges@wcrouse.com

Copyright 1999, Innovators of Today and W. C. Rouse & Son, Inc. All Rights Reserved.

Please send all comments and questions concerning this web site to sales@wcrouse.com