Ambient heat loss

Ambient-heat loss from the external gauge glass or level-trol... 

The gauge glass will normally be somewhat colder than the process vessel as a result of ambient-heat losses (an exception to this would be a refrigerated process). For every 100°F decrease in the gauge-glass temperature or level-trol temperature, the specific gravity of the liquid in the glass increases by 5%. This rule of thumb is typical for hydrocarbons only. Aqueous (water-based) fluids are totally different. 

Note that we have neglected the heat picked up by the steam in the preceding calculation. Often, the steam flow is quite small, compared to the stripper feed, so usually this effect may be disregarded. Unfortunately, we seldom may neglect ambient-heat losses. 

Certainly, if the stripper tower and associated piping are radiating heat from the product, this is not contributing to stripping. To determine the temperature drop due to ambient-heat losses, proceed as follows ... 

The difference between the two temperatures represents the ambient-heat loss associated with the stripper. Of course, with no ambient-heat loss, this temperature difference would be zero. 

If liquid drawn from a column cools below its bubble point, as a result of ambient-heat loss, we say it is subcooled. Mixing a small amount of steam with subcooled liquid, will reduce the partial pressure of any vapor in contact with the liquid, but not enough to promote boiling. Eventually, as more and more steam is mixed with a subcooled liquid, it will begin to boil. But, for a given amount of steam, the amount of vapor that can be boiled out of a liquid will always be less if the liquid is subcooled. In this way, ambient-heat loss reduces the stripping efficiency of steam. 

The heat of combustion is a product of the amount of fuel consumed and the net heating value of the fuel. The heater s efficiency is a function of the flue-gas stack temperature, the excess air or oxygen, and the ambient-heat losses from the firebox and the convective-section structures. 

If the heat picked up from the combustion of the fuel does not equal the heat absorbed by the process fluid, then something is amiss with the data. Often, determining the cause of such an inconsistency will reveal several fundamental operating or measurement problems with a fired heater. Quite commonly, we may find that the metered fuel-gas rate is wrong, or that the ambient-heat losses are much greater than anticipated in our calculations. 

Multiple layers of low conductivity phenolic foam insulation and small temperature differences between the primary coolant and the ambient minimized the heat loss from the primary loop to the ambient. Also, the heat addition to this loop was minimized by using a recirculation pump with an extremely low heat dissipation rate, which was calculated from the pump curves supplied by the manufacturer. With the pump heat dissipation and the ambient heat loss being small fractions of the secondary loop duty, the test section heat load was relatively insensitive to these losses and gains. Local heat transfer coefficients were therefore measured accurately in small increments for the entire saturated vapor-liquid region. Additional details of this thermal amplification technique are provided in the paper by Garimella and Bandhauer [32]. 

Ambient heat loss remains constant regardless of throughput. 

On one 4,000-B/SD crude unit, an energy survey showed 45% of furnace duty was dissipated to ambient heat losses from hot uninsulated lines, manways, etc. 

Reflux pumparound rates can usually be calculated from a heat balance around individual towers. This is the best way to account for unrecorded flows. It is not uncommon for a reflux or pumparound duty, calculated from the tower heat balance, to be 10% to 20% higher than the measured flow would indicate. This is probably due to ambient heat losses. For the sake of consistency of the total test report, it is best to stick with the duties from the heat balance calculations. If the difference between a duty calculated in the two ways described above is much more than 20%, there is a significant error in the test data. 

Alonizing (refinery metallurgy), 427 Ambient heat loss, 30 Amine regenerator reflux drum, 119 Amine regenerator (tray fouling), 392-393... 

Zip informed me that adjusting the steam to the jet fuel stripper did not influence its flash point. That is, the steam was ineffective in removing lighter hydrocarbons (i.e. naphtha) from the stripper feed. This was odd, because the stripper draw temperature was 435°F and the stripper bottoms temperature was 395°F. Typically, a 40°F AT indicates good stripping efficiency. However, when 1 inspected the stripper column, I saw that both the feed line and the stripper shell were entirely without insulation. The 40°F temperature reduction was primarily due to the ambient heat loss. 

Ambient heat loss stays constant regardless of unit throughput. 

Check for ambient heat losses during rainstorm... 

For small package boilers (50,000 Ib/hr), boiler external ambient heat loss is approximately 2 percent... 

The mass flow of flue gas is typically 10 percent greater than the mass flow of combustion air. Without air leaks, but with some ambient heat losses, the following should be approximately true ... 

Ambient heat losses on the flue-gas side can be an important factor in promoting sulfuric acid condensation on smaller units. Ambient heat loss also decreases heater draft due to increased fluegas density in the stack. 

Calculate the observed ambient heat loss from the 20 ft of 3-inch pipe (with an area of 16 fP) using the formula ... 

Divide the observed ambient heat loss (step 4) by the observed sensible heat loss per pound of water. In our example ... 

To illustrate another application, we take an example of a 114-m iminsulated storage tank, 2.74 m in diameter by 19.2 m long, to be filled with 38 m of liquid anhydrous ammonia in a 10-h day, assiuning 21 C required tank temperature (8.0 kg/cm G required pressure), and with an ambient temperature of -34°C. The outside surface area of the tank is 170 m . The convection heat loss can be taken conservatively as 24.4 kcal/h/m /°C at a wind speed of 8.9 m/s. Ambient heat loss is then... 

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