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228                                                                               Boiler Operator’s Handbook


               to block valves and regulators resulting in dangerous  North Africa  which  has  an  air-fuel  ratio  ten  percent
               operating pressures.                                 higher than domestic natural gas. LNG is compressed
                    When water separates from the oil in storage tanks  and cooled until it becomes a liquid; is loaded into tanks
               it settles to the bottom. It will eventually accumulate  aboard ships built exclusively for the purpose; then
               until, all of a sudden, you find yourself trying to burn  transported across the Atlantic Ocean to special port
               water. Water in fuel oil also provides a medium for cor-  facilities near Boston and Baltimore among others.
               rosion of the fuel tank and piping. It’s one of the reasons     Ash in the fuel, whether it’s coal, oil, or biomass
               for leakage of underground storage tanks (USTs) with  can create problems with firing. The ash fusion point is
               some serious consequences. Water can be emulsified (a  the temperature at which the ash melts. If furnace condi-
               process that mixes the fuel and water distributing water  tions produce higher temperatures the ash will melt then
               throughout the oil) but it can still produce corrosion and  solidify again when it cools, usually forming large accu-
               will always require the addition of latent heat to vapor-  mulations of solidified ash that can block air or gas flow
               ize it in the furnace.                               passages or grow in the upper portions of the furnace.
                    Small and controlled quantities of water emulsi-  They grow until they get too heavy to maintain their ad-
               fied in oil can help reduce soot formation which can  hesion to the tubes or refractory and fall crashing to the
               improve heat transfer to the degree it compensates for  bottom of the furnace doing damage to tubes, grates, etc.
               the latent heat loss. When I was sailing for Moore Mc-  When firing fuels with a low (less than 1800°F) ash fu-
               Cormack Lines in the 1960’s we were conducting an ex-  sion temperature the operator has to monitor the furnace
               periment with injecting small quantities of superheated  conditions inspecting it and recording draft readings to
               steam into the fire to reduce sooting. I never did find out  detect hardened ash accumulations early.
               what the results of that were.                           One of my projects included burning dust from a
                    Water in fuel gas systems can be a considerable  laminate sanding operation where portions of the ash
               problem when the gas pressures are low because it can  had very low fusion temperatures. We operated that
               collect and produce blockages in the piping as well as  boiler at very high excess air just to keep the furnace
               promote corrosion. When you have wet fuel gas you’ll  temperatures down to prevent the ash melting and
               have additional requirements for handling the liquids  sticking to the tubes. Someone advised that customer
               that settle in your piping because there can be liquid  they could save a lot by decreasing excess air (true in
               fuels as well as water. Water draining from a coal pile is  other situations) so they did; and ended up with huge
               highly corrosive and must be discharged to a sanitary  globs of solid ash stuck to the furnace walls and tubes.
               sewer after it is neutralized.                           You should always know what the vanadium con-
                    The  discussion  in  the  chapter  on  combustion  tent of your fuel is because that material produces a lot
               helps explain why firing conditions change when the  of low melting point ash. Just last week I spent a Satur-
               fuel changes. Most of the time the air-fuel ratio is close  day evening crawling into a boiler to see the result of
               enough to ignore the variations. When a service techni-  blockage due to low melting point ash. The customer’s
               cian uses a portable analyzer to calculate combustion  fuel oil only had about 30 ppm of vanadium in it but was
               efficiency that analyzer contains a “typical” fuel analysis  enough to completely block up the first pass of the boiler
               for the fuel and determines efficiency based on that typi-  with ash that took about two days to clean with a high
               cal analysis. I’ve always wondered if those analyzers  pressure washer.
               are calibrated for the area because the carbon content
               of natural gas can vary from 20.3% to 23.5% between
               the east and west of the country. That amounts to a 15%  FUEL GASES
               variation in higher heating value of the fuel and it’s one
               reason I refuse to believe the efficiency on one of those     Natural gas is mostly methane (CH ) with portions
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               machine’s printouts. It’s only important that you know  of other flammable gases, oxygen, carbon dioxide, and
               that the analysis can change and have an equal distrust  nitrogen. A typical volumetric analysis is 96.53% meth-
               of those electronic analyzers’ efficiency indications.  ane, 2.38% ethane, 0.18% propane, 0.02% iso-butane,
                    In the Baltimore area we can experience changes  0.77% carbon dioxide, and 0.12% nitrogen. That’s east
               in natural gas depending on the source of the gas in  coast gas. Gas constituents will vary depending on the
               Pennsylvania, Texas or Louisiana and the blending of  well the gas came from. When a boiler is fired with oxy-
               gases from those sources. We also have a chance to burn  gen trim controls to achieve very small quantities of ex-
               some of the LNG (liquefied natural gas) imported from  cess air those controls accommodate the varying air-fuel
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