PAT Normalisation: The need
Comparing the Specific Energy Consumption (SEC) or Energy Performance Indicator (EnPI) in the assessment year against the baseline year within boundary limit is a simple way of measuring the progression in energy performance of a plant taking into account the measured value of Energy and Production between two different periods. Specific Energy Consumption (SEC) is one of the energy performance indicators of a process and is defined as net energy consumed in tonne of oil (toe) for making per tonne of equivalent product. Similarly, Energy performance Indicators (EnPI) of a thermal power station is the Heat Rate of power generation and is defined as thermal energy consumed in kcal to generate a kWh of electricity. However, there are several factors that need to be taken into consideration to make a meaningful and logical comparison. Factors like change in product mix, capacity utilization, change in raw material or fuel quality, import/export of electricity etc. are few examples that can make this comparison difficult. Depending on how these factors change over the assessment period, the Designated Consumers (DCs) may sometimes get undue advantage or may get penalized for no fault of theirs. Normalisation, therefore, is a way to overcome the above problem and can be defined as a process of rationalization of Energy and Production data of an establishment to take into account, the changes in quantifiable terms that impact energy performance under equivalent conditions over the assessment period.
What are quantifiable variables:
The energy performance of a process is dependent on quantifiable variables, which are required to be normalized so that that the actual energy performance could be quantified/compared. These variables impact the energy performance of a plant and may include factors like change in production or generation rate in terms of capacity utilization or plant load factor (PLF), start-stop of major equipment due to non-availability of fuel/raw material, start-stop of a section or even plant can also occur due to unforeseen circumstances such as natural calamity, social unrest, labour strike, lock outs etc. The change in SEC do occur in corresponding periods depends upon multiple products apart from the major product made in series and parallel process production called Product Mix Normalisation along with import (Sale) and export (Purchase) of Products known as Intermediary Product normalisation
Changes in raw material and fuel quality, power mix (import and export of power), fuel mix, product mix are other major factors that influence the energy performance as well.
The other factors that relates to the installation of equipment in the assessment year due to Environmental Concern, Installation of New section/Line/unit, Energy used for Project Activities, etc do influence the SEC of Plant. The factors over which an individual DC does not have any control but that can impact the SEC are classified as uncontrollable factors and needs to be normalised in the assessment year.
For a process plant, the decrease in SEC shall only be observed w.r.t. the increase in production rate( Chlor-alkali Sector being exceptional) or through energy savings achieved after implementation of Energy Saving measures or projects.
In today’s blog, let me highlight the factor of Production Rate and Capacity Utilization. The production rate of a process/unit/plant shall always be more than the capacity utilisation for the same period. Due to decrease in production rate, the energy performance of a plant will also deteriorate i.e., energy rate will increase and this indicates that the production rate do have a relationship with energy performance. However, to establish a relation between the energy performance and Production rate, some methodology needs to be adopted i.e. either to have a statistical method from the OEM’s design data or to have statistical approach through filtered multiple operating data of Energy and Production rate.
Both these approaches have inbuilt difficulties. The first approach requires design data from the OEM, which is generally not available. This means, for making a standard methodology of normalisation on capacity utilisation, the design data at different production rate should be simulated in software for arriving at a Normalisation equation or with the help of nos of design data plotted through a graph from function of Energy and Production rate. This methodology has been followed in CPP-PLF normalisation in all the sectors, while respective OEM curve on loading vs heat rate was followed in Thermal Power Plants.
To determine and standardise a relation between Production rate and SEC through operating data, it is important to use only normal operative data and avoid abnormal operative parameter, so that a meaningful correlation could be developed between the two variables. Since, operating data do carry plant inefficiencies like variation due to raw material quality, start and stop, thus chances of duel benefit could not be negated. A careful approach of gathering the filtered data may result in a standard curve, which could be further strengthened through selecting the parameter more judiciously on similar line and making the appropriate equation after plotting the characteristics curve.
Product Mix is another classic example of normalising the multiple products into a major one, which I will be discussing in my next blog.
Mr. Vikash Ranjan