AEUB Updates the Noise Control Directive ID 94-4
The AEUB is currently in the final drafting stages of the update for the Noise Control Directive (currently Interim Directive ID 94-4). In summary, it appears that the changes to this Directive will be somewhat cosmetic. Residences in certain Fort Saskarchewan areas will get particular attention to their unique zoning parameters. From a technical perspective the main addition will be a caution to engineers generating noise impact assessments to be aware that simple extrapolation of the noise levels from the "1 metre measurement" to nearest residences, is not that simple.
In the vast majority of cases the simple square law equations are not applicable from the one metre measurements and it is usually necessary to convert the sound pressure levels (SPL) to sound power levels (PWL), then back to SPLs at the residences.
Some simple modelling methods were presented at the AEUB Spring Conference 1998 in the paper "Modelling of Common Noise Sources" by Richard Patching of our firm.
In the past Patching Associates Acoustical Engineering Ltd. has condeucted numerous in-house seminars for our clients explaining the details of the Noise Control Directive and giving practical ideas and examples of how to rectify existing problems and how to avoid the likelihood of these environmental problems.
Given the expected changes in the Noise Control Directive, Patching Associates would be happy once again to provide these in-house seminars (usually a one hour lunch bag session) for our engineering clients where 6 or more engineers and technologists express an interest. We are therefore enclosing an information sheet which we would ask clients to return to us indicating your interest in one of these free seminars. Any questions on the seminars or any items addressed in this newsletter may be directed to either Richard Patching or Nev Hircock at 274-5882.
Process Heat Sinks
As we approach summer, it is time for many operators
to consider how to avoid high temperature shut downs on their compressors,
engines, refrigeration condensers and other plant cooling systems. Before
even addressing whether the existing plant coolers are operating optimally,
a more basic question is whether or not the processing plant is using
the most appropriate heat sink.
What is a Heat Sink?
A heat sink for a process plant can be defined as a fluid with a massive thermal capacity at a temperature below which we wish to cool plant process streams. For most Alberta plants this is simply atmospheric air. Where river water or lake water is available this is a much better heat sink because it is:
- usually some 20ºF cooler than air in the summer
- a substantially better heat transfer medium.
However, many processing plants may also use two other excellent heat sinks which are often overlooked. These are:
- Incoming plant raw gas. This usually arrives at mean ground temperature which is usually some 25 - 35ºF cooler than atmospheric air on a hot day.
- Disposal Water. This is an excellent heat sink usually available at oil processing plants which are subject to a high water/oil ratio.
What Are The Benefits of Water Over Air Cooling?
When water is available (whether it's river water, lake water or disposal water) it is a substantially preferred heat sink over atmospheric air. Firstly the typical water cooled shell and tube exchanger will cost less than half that the price of a comparable fin/fan aerial cooler. Secondly water temperatures usually do not exceed 70ºF in the summer compared to ambient air which may reach 90ºF. The water cooler exchange approach temperature is also better than that achieved by aerial coolers, with the result that process streams cooled by water will be typically 25ºF cooler than the same stream cooled by air on a hot summer's day. In the case of gas compressor intercoolers, every 5ºF improvement on temperature equates to an increased throughput of 1%. Therefore 25ºF on a hot day amounts to a 5% plant debottlenecking. In the case of refrigerant plant condensers the benefits of water over air are magnified. A refrigeration system using a water condenser will use approximately 20% less power than the same system using atmospheric air. Below are three examples of recommendations made to clients over the past year for improved cooling systems using innovative heat sinks - other than atmospheric air.
The first two process sketches illustrate the use
of disposal water as a heat sink either as a plant refrigerant condenser
or as a supplemental cooler for overheating engines where the existing
radiator is inadequate. Ineither of these examples, a relatively inexpesive
low pressure shell and tube or plate frame exchanger can be used. Figure
1 illustrates the use of incoming raw gas as a heat sink to cool compressor
aftercooler discharge gas. This is quite ofter useful in remote plants
where electricity is not available to add supplementary aerial cooling
and where gas flowing to the dehydrator is too hot to effectively meet
dew point. This system has one slight diadvantage in that the intake
gas to the compressor is, of necessity, preheated. This may reduce the
compressor capacity slightly.
Can I Spray Water Directly Over Existing Aerial Coolers to Enhance Performance?
Yes, this has a very distinct short term effect on the cooling capacity of the fin fan unit. However it is not recommended if you plan on keeping the plant for more than a few years. Spraying untreated water direct on fin tube has three serious negative effects:
- The untreated water evaporates off the fins and leaves salt caked between the fins which is virtually impossible to remove later.
- The water causes dielectric corrosion between steel tube and aluminum fins.
- The water thermally "shocks" the fins causing them first
to bind tighter on the steel tube and then to release in yield once
the spraying stops. This causes fin delamination and loss of bonding
between the aluminum fin and the steel tube.
