Chemical Engineering @ChemengFiles.Com

The rates of heat and mass transfer from equilibrium non-spherical n-heptane drops in an air stream have been investigated. Two types of drops were produced, one wetting the supporting tube and another not wetting the supporting tube. The drops ranged from 0.005 to 0.008 ft in diameter. Measurements were made at bulk air velocities between 2 and 8 fps, with an air temperature of 100?F. A semi-empirical relation taking into account the deviation of drop shape from spherical leads to a satisfactory correlation of data with those obtained by other investigators for spherical drops.

Energy efficiency for industrial boilers is a highly boiler specific characteristic. No two boilers are alike. There are two identically designed, constructed side by side, stoker fired boilers in Indiana burning the same fuel that have very different performance characteristics. Like twin teenagers, they are not the same.

Consideration of energy efficiency for industrial boilers, more often than not, is simplified and categorized to a one-size-fits-all approach. Just as when considering teenagers, this does not work. While everyone would like to believe their teenager is gifted and talented and in the 80th percentile of the population, we know that is not necessarily the case.

We also know, as for boilers, the average teenager is not representative of a widely diversified population. If you think it is, ask any parent with teenagers or an industrial boiler operator. While the variables associated with energy efficiency are more limited than those associated with a teenager, they are in no way any less complicated.

Four factors are critical for assessing energy efficiency in the industrial powerhouse supplying energy to make products for the benefit of customers in a highly competitive international market place. These are:

1. fuel type,
2. combustion system limitations,
3. equipment design, and
4. steam system operation requirements.

Furthermore, the industrial facility’s complexity, location, and objective complicate them. It is important for the industrial company to remember, unlike the utility, energy is a smaller portion of the final product price. However, without energy there is no final product or service. Needless to say, without products or services there is no need for people to do the work.

Today’s process and heating applications continue to be powered by steam and hot water. The mainstay technology for generating heating or process energy is the packaged firetube boiler. The packaged firetube boiler has proven to be highly efficient and cost effective in generating energy for process and heating applications.

Conducting a thorough evaluation of boiler equipment requires review of boiler type, feature and benefit comparison, maintenance equirements and fuel usage requirements. Of these evaluation criteria, a key factor is fuel usage or boiler efficiency.

Boiler efficiency, in the simplest terms, represents the difference between the energy input and energy output. A typical boiler will consume many times the initial capital expense in fuel usage annually. Consequently, a difference of just a few percentage points in boiler efficiency between units can translate into substantial savings. The efficiency data used for comparison between boilers must be based on proven performance to produce an accurate comparison of fuel usage. However, over the years, efficiency has been represented in confusing terms or in ways where the efficiency value did not accurately represent proven fuel usage values. Sometimes the representation of “boiler efficiency” does not truly represent the comparison of energy input and energy output of the equipment.

This Efficiency Facts Booklet is designed to clearly define boiler efficiency. It will also give you the background in efficiency needed to ask the key questions when evaluating efficiency data, and provide you with the tools necessary to accurately compare fuel usage of boiler products, specifically firetube type boilers.

Remember, the initial cost of a boiler is the lowest portion of your boiler investment. Fuel costs and maintenance costs represent the largest portion of your boiler equipment investment. Not all boilers are created equal. Some basic design differences can reveal variations in expected efficiency performance levels. Evaluating these design differences can provide insight into what efficiency value and resulting operating costs you can expect. However, every boiler operates under the same fundamental thermodynamic principles. Therefore, a maximum theoretical efficiency can be calculated for a given boiler design. The maximum value represents the highest available efficiency of the unit.
If you are evaluating a boiler where the stated efficiencies are higher than the theoretical efficiency value, watch out! The efficiency value you are utilizing may not truly represent the fuel usage of the unit.

Continuous distillation processes are frequently characterized by uncertainties of their inflow. These may relate to the flow rate, to the composition of the mixture to be separated or to its temperature. Typically, the uncertainties are not completely irregular but follow a certain pattern caused by the operation of upstream units. Then it makes sense to model uncertainty as a stochastic parameter, the distribution of which can be estimated from history but the realization of which in the coming period of optimization is unknown. In the following, we are going to consider the rate of inflow as the only random parameter. As a consequence of possible unpredictable peaks, the inflow cannot be processed immediately but has to be stored in a feed tank before being directed at a controlled rate to the distillation unit (see [9], Figure 1). For technological reasons, one has to impose upper and lower level constraints for the feed tank preventing it from running full or empty. Both cases would require unpleasant compensating actions which are desirable to avoid (see [9], Section 1.3). Therefore, a problem will be formulated which reflects the objective to find a feed control being robust with respect to level constraints yet optimal in the sense of minimum energy consumption subject to product specifications.