Why maintaining boiler efficiency is crucial?
In case of boilers, cost of buying a new boiler is small compared to the amount of money spent in operating the boiler year on year. The following diagram shows the break-up of total cost of ownership for both oil/gas fired boilers and solid fuel fired boilers. It can be easily noticed that the fuel cost is the biggest contributor in the overall ownership cost for both oil/gas and solid fuel fired boilers.
Amount of money spent on fuel is closely related to the efficiency of the boiler. Although boiler efficiency is an important parameter in the boiler specification when buying a new boiler, little attention is given to it once the boiler is steaming. The myth is that boiler will always continue to generate fuel at its rated efficiency. Truth is, the actual delivered boiler efficiency tends to be lower than 3%-12% than the rated efficiency.
A survey conducted by CII shows that scope of savings in boiler house ranges from 28% to 46% for different industries (out of total scope of savings in the entire steam and condensate loop).
At the same time, as following illustration clarifies, steam consumption increased by 16% when boiler efficiency dropped by 10%.
This makes putting check on boiler losses even more crucial.
The cost of steam generation has gone up by almost 2.5 times in the last decade. The cost of generating steam using a solid fuel fired boiler today is greater than an oil fired boiler ten years ago. In the next sections of this article, we will explore how online efficiency monitoring can help us to tackle the situation in a much better way.
Online boiler efficiency monitoring- Why is it important?
It can be observed that the efficiency of a boiler is not static- but it is dynamic. Users take it for granted that the boiler is operating at the rated efficiency. Monitoring across large number of boiler houses shows that there are many variations which affect the boiler efficiency. It is important to adjust the boiler for these variations regularly to ensure optimum boiler performance.
A few of the factors which affect boiler performance are :
1. Shift variations
Typically in plants, load pattern changes from shift to shift. If the boiler response to these load variations is not changed, the efficiency of the boiler drops. The required changes in settings can be as simple as changing firing rate or pressure limit of the boiler. The changes can be easily done from the boiler control panel itself in oil, gas or solid fuel fired boilers. Online efficiency monitoring helps to identify what needs to be changed at what time.
2. Daily variations
Load variations may occurs from day to day too. Again, the boiler needs to be adjusted to cater to this efficiently.
3. Weekly variations
As the fuel quality is changing continuously, adjustments need to be made to the combustion system to take care of these variations. In oil or gas fired boilers, the quality of oil being received may vary from tanker to tanker. The moisture content in solid fuel changes from time to time and the source of purchase. This changes in fuel quality makes adjustments necessary.
4. Seasonal variations
Boiler loading pattern is an important factor here too. The production requirement of the plant may be affected by seasonal demands. This calls for adjustments again. In solid fuel fired boilers, the fuel available may change depending on the seasons. The ambient air temperatures and humidity will also change from season to season. The combustion system needs adjustment too.
Online efficiency monitoring – How does it help?
Online boiler efficiency monitoring works through measuring several critical parameters. Some of the measured parameters are- stack temperature, steam temperature, feed water temperature, combustion air (inlet) temperature, Stack oxygen, furnace pressure, steam flow, fuel flow, blowdown, blowdown TDS etc.
The strength of online monitoring is not only limited to measuring the parameters as they also calculate different losses, efficiency and generate valuable trends and analysis. The losses which such systems can calculate include blowdown losses, radiation losses, and enthalpy losses and stack losses.
Efficiency and Steam: Fuel Ratio Calculation
Real time efficiency monitoring makes available its users the boiler efficiency at any time. This helps the plant personnel to relate any changes in the boiler efficiency to the reasons behind the changes. This particularly helps in identification of factors which are preventing the boiler from running at the optimum efficiency and hence help the personnel to take the correct action.
Patterns/ Trends and Analysis
Many times, observing data over a long period of time can give valuable insights. Observing trends and pattern of a boiler over months can help to spot important trends and take diagnostic actions. It is good to have a real time monitoring system which intelligently suggests corrective action by analysing the trends over a long period.