Normally when buying a new steam boiler, one of the first parameters that are evaluated is its efficiency.
This is because it represents the effectiveness of transforming the energy of the burned gas into steam.
However, the single boiler&#;s efficiency is not everything.
If you either need to decide which boiler is the best fit or achieve a reasonable improvement in performance and therefore savings in consumption, you must evaluate the overall efficiency of the thermal power plant.
But let&#;s go in order and see what the efficiency of a steam boiler is.
What is the efficiency of a steam generator?
Why is boiler efficiency important?
Calculation of the average yield and savings on gas consumption:
a. The real efficiency;
b. Start with demand profiles
c. How to save with performance
Conclusions
When it comes to calculating the efficiency of a steam generator, there are many variables to consider.
It is not very intuitive and some clarifications are needed, before going any further.
Let&#;s start from the basics:
What is meant by the efficiency of a steam generator? How is it calculated? Why is it classified as the most important parameter of a thermal power plant?
Let&#;s go in order and answer the first question: what is meant by the efficiency of a steam generator?
The efficiency of a steam generator is nothing more than a measure of its energy efficiency: it is the percentage of energy generated by combustion, energy which is then transferred to the water to evaporate it. In the calculation, it is also necessary to take into consideration the energy lost in dissipations, and fumes deriving from combustion.
As the dissipations and the temperature of the fumes decrease, the efficiency will always be higher: it will tend to 100%, without ever reaching it.
For the principles of thermodynamics, the 100% efficiency is impossible to achieve, as the heat generated by combustion would be transferred entirely to the water, without causing the slightest dispersion.
It is intuitive to say that, as the efficiency of a steam generator increases, the amount of fuel (e.g. natural gas) required to produce it will decrease.
After having made an overview on the meaning of efficiency, let&#;s move on to the study of a practical case, in which we show its correlation with methane consumption, and then go on to understand how to decrease it.
In order to understand how important the calculation of the steam generator real efficiency is, we analysed the operating costs of a thermal power plant in its first 10 years of life.
We then divided all costs into the initial investment, natural gas consumption, electricity, water and maintenance costs.
This is what we found out.
What is noticeable at first glance, is the preponderance of methane costs compared to all the others.
In this case, about 68% of the total costs are represented by methane; and it is precisely here that we want to dwell.
Since efficiency is the ability to transfer the heat produced by combustion to water, and then transform it into steam, the higher the yield, the less volume of methane is needed to produce a certain amount of steam.
Since methane is the highest cost item for a heating system, and since efficiency is the parameter that most affects its consumption, it is now clear why is so important when choosing the new boiler.
Let&#;s see how it is calculated and how the boiler manufacturers use it in their favor, not behaving in a completely transparent way.
The efficiency of a steam boiler is always provided by the manufacturer. All of them though calculate the efficiency under particular conditions that not always match the real ones.
So the question now is, what are those conditions? How does the efficiency vary based on mine?
Often, the customer who decides to buy or replace a boiler is not aware of the fact that the data provided by the manufacturing company is processed in the laboratory under specific loading conditions.
A bit like the automotive market, where the promised consumptions are almost impossible to achieve in our everyday life. The same thing happens in the world of industrial steam boilers.
So how do we move between unrealistic returns and technical specifications that are not entirely authentic, and not calculated based on our system?
Here are some tips.
As mentioned in the previous paragraph, the yield provided by the manufacturer is calculated based on certain conditions recreated in their laboratory
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Normally those parameters are, power close to 100%, ambient temperatures around 25 degrees and feed water temperatures close to 80 degrees.
As these conditions change, the efficiency of the steam generator varies accordingly.
So what do you need to do?
It becomes crucial to know and calculate efficiency according to the actual working conditions for your thermal plant.
This will allow you to simulate the cost of your system and find solutions to contain them.
Normally steam requests throughout the working day or season vary following demands from production lines.
Here in the chart below, we have studied this variation on the specific case of one of our customers, in which it is seen how the flow of steam and its pressure vary throughout the day.
In addition to these data, to calculate the efficiency of our generator it will be necessary to detect the ambient and inlet water temperatures, in this way we will be able to calculate the true efficiency of the heating system and therefore the methane consumption.
Starting from these conditions, diverse solutions can be found to increase the average efficiency and decrease costs: for example, by increasing the modulation range of your boiler.
If you need support in calculating performance and analyzing plant data, fill out the form at the bottom of the page.
At this point, we start to have a solid understanding of what is the steam boiler efficiency.
But how can we use this information to guide us in choosing a new generator? How does the choice of generator affect methane expenditure throughout its life?
Taking up the concept expressed at the beginning of the article, methane represents approximately 68% of the total costs of a heating system under the conditions established previously.
When we have to choose between different boilers, priority must be given to what allows us to reduce methane consumption as much as possible.
Often this translates into higher initial costs, but even just a 1% increase in efficiency will allow you to save around &#; 5-6,000 each year only on methane costs.
So what tools can you use to increase the average efficiency of your thermal power plant?
Considering the profiles of steam flow and pressure requirements, it is better to look for the boiler and burner that best modulate and &#;follow&#; the required load, thus avoiding unnecessary waste.
Depending on the pressure profile, it is also advisable to choose a system that can modulate the steam pressure supplied.
The higher the modulation ranges for the flow rate and the steam pressure, the higher the average efficiency of our system, with consequent savings in burnt methane.
The reduction in consumption often means more expensive technologies, but, almost always, widely justified by the economic savings received every year.
The efficiency of a steam boiler is undoubtedly the parameter that we all know best, as well as the most important, as it is the percentage of energy efficiency that a generator can achieve.
As the efficiency increases, the dissipations and dispersions will decrease and it will cost less and less to produce steam.
Given its importance and centrality, many boiler manufacturers &#;inflate&#; this number, by creating it in the laboratory conditions that are not easily replicable.
For this reason, it is important to collect the flow and pressure profiles of our system, to then calculate the efficiency according to your real conditions.
Starting from the analysis of these profiles, we can then identify the steam boiler with specifications that allow us to increase the average efficiency of the entire system and decrease methane consumption.
If you need further clarification on the calculation of your real efficiency, do not hesitate to contact us and request a free inspection.
Annual Energy Use: 1,400 full-load hours per year, for 25 years.
Annual Energy Cost: Calculated based on an assumed natural gas price of 8.48¢ per therm, which is the average price at federal facilities in the United States (Site-Delivered Energy Use by End-Use Sector and Energy Type in Fiscal Year ).
Lifetime Energy Cost: Future electricity price trends and a 3% discount rate are from the Energy Price Indices and Discount Factors for Life-Cycle Cost Analysis &#; : Annual Supplement to NIST Handbook 135 and NBS Special Publication 709 (NISTIR 85--39).
Lifetime Energy Cost Savings: The difference between the lifetime energy cost of the less efficient model and the lifetime energy cost of the required model or best available model.
Calculated based on highest efficiency model identified in publicly provided manufacturer data as of June . Note that more efficient models may be introduced to the market after FEMP's acquisition guidance is posted.
Calculated based on FEMP-designated efficiency requirements. Federal agencies must purchase products that meet or exceed FEMP-designated efficiency levels.
Calculated based on the current federal minimum efficiency standard for this product type.
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