BHUTANI NAVEEN (IN)
MATHUR TARUN PRAKASH (IN)
BHUTANI NAVEEN (IN)
WE CLAIM: 1. A method for energy benchmarking for process plant having at least one equipment, wherein the said method comprising the steps of: adapting a process model for the said process plant; determining energy consumption of the said process plant based on design conditions and / or current operating conditions; and performing optimization for estimating energy benchmark. 2. A method for energy benchmarking for process plant having at least one equipment, and for diagnosing the said process plant thereof, wherein the said method comprising the steps of: adapting a process model for the said process plant; determining energy consumption of the said process plant based on design conditions and / or current operating conditions; performing optimization for estimating energy benchmark; calculating indices for gap analysis; and diagnosing the gap between the said current energy consumption of the said process plant and the said estimated energy benchmark. 3. The method as claimed in claim 1 or 2, wherein the step of adapting the said process model include relating the energy consumption of the said process plant to the process conditions. 4. The method as claimed in claim 1 or 2, wherein the step of determining energy consumption further comprising employing design conditions such as design values of the said process plant that corresponds to yield and / or energy coefficients. 5. The method as claimed in claim 1 or 2, wherein the step of determining energy consumption further comprising employing current operating conditions such as current operating values of the process variables of the said process plant and that corresponding to yield and / or energy coefficients. 6. The method as claimed in claim 1 or 2, wherein the step of performing optimization for estimating energy benchmark further comprises using constraints of the equipment and / or the said process plant and / or using the said process model for estimating energy benchmark. 7. The method as claimed in claim 2, wherein the step of diagnosing the gap includes using the said indices for reducing the gap between the said current energy consumption of the said process plant and the said estimated energy benchmark. 8. The method as claimed in any one of claims 2 to 7, wherein the step of diagnosing comprises comparing the values purporting to yield and / or energy coefficients of design conditions and / or of current operating conditions and / or that of current process variables, correspondingly with the values of yield or energy coefficients or process variables obtained through optimization. 9. The method as claimed in claim 8, wherein the step of diagnosing further comprises controlling the said equipment and / or the said process plant accordingly based on the said comparison and improvement thereupon through maintenance and / or operation of the said equipment and / or the said process plant. 10. A system for energy benchmarking for a process plant having at least one equipment, and diagnosis thereof, in accordance with the method as claimed in any one of the preceding claims, the said system comprising: a process model of the said process plant; an energy consumption determination component to determine energy consumption of the said process plant based on design conditions and / or current operating conditions; an optimization module to perform optimization for estimating energy benchmark; a diagnosis module to calculate indices for gap analysis and accordingly to diagnose the gap between the said current energy consumption of the said process plant and the said estimated energy benchmark. |
THROUGH OPTIMIZATION AND A SYSTEM THEREOF
FIELD OF THE INVENTION
The invention relate to a method and a system for energy benchmarking for process plant, and more particularly to energy benchmarking and diagnosis through optimization. BACKGROUND
Generally, in a process industry or plant, energy is consumed in various forms like steam, electricity etc, for its functioning and for producing the yield or product. The consumption of energy in a process plant needs to be monitored and compared against a reference value and thereupon contribute towards improving the efficiency of the plant. The method of obtaining the reference value is termed as benchmarking.
Currently, benchmarking is done using several methods, more popular among them are statistical method and thermodynamic method. In statistical method, data relating to plant operation i.e. the historical operating data and patterns of energy consumption corresponding to multiple plants employing similar process technology are obtained and analyzed for the most energy efficient one and is being set as the benchmark. In thermodynamic method, best possible energy efficiency of the plant is computed theoretically and is set as benchmark.
Both the aforementioned, statistical and thermodynamic methods have notable limitations. Statistical method require recent and extensive data from multiple plants and as such do not take into account the effect of the operating conditions, external factors like climate, age of plant, scale of operation etc on the performance of the plant. Apparently, it is probable that a plant which is energy inefficient be set as a benchmark due to the limited survey of plants and /or limited availability of plants during survey. Further, even the plant considered to be most energy efficient may be farther away from its best / design performance, and require improvement that cannot be predicted by this method. On the other hand, thermodynamic method often set benchmark for energy efficiency which is unrealistic due to the fact that it does not give due consideration for practical limitations in the processes such as constraints purporting to quality, design, age of plant/equipment etc.
Moreover, in the current practice, though energy benchmark is set, the same cannot be realized in the plant due to the practical limitations that persists and that being not accounted for in setting benchmark. Hence, there is a need to have an approach to set energy benchmark considering the practical limitations of the plant and provide a solution that enables the plant to work closer or reach the energy benchmark that been set.
OBJECTS OF THE INVENTION
It is an object of the invention to provide a method for energy benchmarking for a process plant, where the said energy benchmarking is realistic. It is another object of the invention to provide a method for energy benchmarking which suggests recommendation that enables the process plant to improve with regard to energy consumption.
It is also another object of the invention to provide a system for and capable of performing the method according to the invention. SUMMARY OF THE INVENTION
In accordance with one aspect of the invention there is provided a method for energy benchmarking for process plant having at least one equipment. The method comprising the steps of: a) adapting a process model for the said process plant. Adapting the process model herein refer to one or more of developing a process model for a process plant or using an existing process model without alteration or adapting an existing process model to suit the said process plant. Adapting the process model includes relating the energy consumption of the said process plant to the process conditions; b) determining energy consumption of the said process plant. This is done based on design conditions and / or current operating conditions. Design conditions include but not limiting to values of the said process plant and corresponding to yield or energy coefficients or both. Current operating conditions include but not limiting to current operating values of the process variables of the said process plant and correspond to yield or energy coefficients or both; and c) performing optimization for estimating energy benchmark. Performing optimization for estimating energy benchmark further comprises using constraints of the equipment or the said process plant or both for estimating energy benchmark.
In accordance with another aspect of the invention there is provided a method for energy benchmarking for process plant having at least one equipment, and for diagnosing the said process plant thereof. The method according to this aspect of the invention comprises the steps of the method described herein above. Additionally, the method comprises the steps d) calculating indices for gap analysis; and e) diagnosing the gap between the said current energy consumption of the said process plant and the said estimated energy benchmark. Diagnosing is done using the said indices for reducing the gap between the said current energy consumption of the said process plant and the said estimated energy benchmark. Also, diagnosing includes comparing the values purporting to yield and / or energy coefficients of design conditions and / or of current operating conditions and / or that of current process variables, correspondingly with the values of yield or energy coefficients or process variables obtained through optimization. Diagnosing further refers to controlling the said equipment and / or the said process plant accordingly based on the said comparison and improvement thereupon through maintenance and / or operation of the said equipment and / or the said process plant. It is to be construed that diagnosing mentioned herein is not restrictive to that been stated here above.
According to yet . another aspect of the invention there is provided a system for energy benchmarking for a process plant having at least one equipment, and diagnosis thereof. The method of performing energy benchmarking and diagnosis as mentioned above is in accordance with the invention. The system of the invention is capable of and for performing the method according to the invention. The system of the invention comprises: a process model of the said process plant; an energy consumption determination component to determine energy consumption of the said process plant based on design conditions and / or current operating conditions; an optimization module to perform optimization for estimating energy benchmark; and a diagnosis module to calculate indices for gap analysis and accordingly to diagnose the gap between the said current energy consumption of the said process plant and the said estimated energy benchmark. The indices for gap analysis may be calculated in a separate module either explicitly or implicitly. The system can also include one or more suitable controllers for the purpose of diagnosing or the like by way of controlling the equipment and / or the process plant.
BRIEF DESCRIPTION OF THE DRAWING
With reference to the accompanying drawings in which:
Fig. 1 shows a schematic representation of energy benchmarking and diagnosis in accordance with the method of the invention.
Fig. 2 shows a simplified material flow diagram for Basic Oxygen Furnace.
DETAILED DESCRIPTION
The invention is described hereinafter with reference to an exemplary embodiment for better understanding and it is non exhaustive in nature. The invention relate to a method for energy benchmarking of process plant and also to perform diagnosis thereto in relation to the said energy benchmarking.
It is to be understood that the current practices do not give due consideration for the constraints prevalent with respect to the equipment and/ or the process plant. It would be appreciable if energy benchmarking is done in a realistic manner taking into considerations these drawbacks, and the invention provides a solution to this effect.
The invention is further explained with reference to an exemplary schematic shown in Fig. 1. The performance assessment component (101) performs the assessment of the performance relating to equipment / process plant, based on which it is to be seen whether energy benchmark need to be performed for any particular equipment / process plant. This can be done in multiple ways, some of which are, based on the process knowledge of the operator, comparison of actual performance of the equipment / process plant with corresponding design performance. Accordingly the need for energy benchmark and / or diagnosis thereafter is decided upon. However, this step of performance assessment is optional and is not mandate. A process model (102) is developed or an existing process model is used as such or an existing model is adapted to suit the process plant. One or more of this refers to adapting a process model for the process plant in the context of the invention. Adapting the process model means relating the energy consumption of the process plant to the process conditions. The energy consumption is expressed as a function of process variables, yield and energy coefficients. The values of the yield and coefficients may again be a function of process variables. The simplified equations are given as below:
Energy consumption = f (process variables, yield, energy coefficients) (1) Yield = f (process variables) (2) Energy coefficients = f (process variables) (3) The energy consumption is determined by the energy consumption determination component (103) with respect to design conditions and current operating conditions of the process plant and is represented as E < jes and E cmTen t, respectively. The design condition includes design values of the process plant that corresponds to yield and / or energy coefficients. Similarly, current operating conditions include current operating values of the process variables pertaining to the process plant and that corresponding to yield and / or energy coefficients. The values of yield and energy coefficient corresponding to design conditions are represented as Yieldjes and EnergyCoeff des, respectively. The values of yield and energy coefficient corresponding to current operating conditions are represented as Yield cUITe nt and EnergyCoeff cuiren tj respectively.
Optimization for estimating energy benchmark for the process plant is performed by the optimization module (104). The optimal values of the process variables, yield and energy coefficients are found and are represented as Process variables op t, Yield opt and EnergyCoeff op t, respectively. Optimization is performed to find out the optimal energy consumption for the process plant, accounting for the practical constraints on the equipment and / or the process plant. The optimal energy consumption so obtained under the realistic constraints is the energy benchmark estimated for the process plant. Indices ki to k 5 are calculated for gap analysis. These indices are used in performing diagnosis for the gap between the current energy consumption of the process plant and the estimated energy benchmark. Equations relating to finding ki to k 5 are shown below:
(Yields -Yield ^ )
Yield o.pt
(Yields - Yield opl )
Yield des
(EnergyCoeff opl - EnergyCoeff^, )
Energ Coejf opt
(EnergyCoeff des - EnergyCoeff opl )
EnergyCoeff des
Diagnosis for the gap between the current energy consumption of the process plant and the estimated energy benchmark is performed by the diagnosis module (105). As a part of it, an approach to reduce the gap between the current energy consumption of the process plant and the estimated energy benchmark is deduced, where recommendation for reduction of such gap is made. ki or k 3 being greater than a predefined value signifies that the current yield or energy coefficient, respectively, of the process plant is far from their corresponding optimal values. This means that there is a need for improvement through operation for the said process plant in order to improve the energy consumption of the said process plant and bringing it close to or at the energy benchmark that been estimated. To attain this, the process plant is operated as per the values of process variables obtained from optimization (Process variables opt ). Similarly, when k 2 or being greater than a predefined values signifies that the optimal values of the yield or energy coefficient, respectively, of the process plant within the given operational constraints is far from their corresponding design values. This could be due to the aging of the process plant and requires maintenance. Accordingly improvement through maintenance can be carried out to reach the estimated energy benchmark. Alternatively, k 2 or IQ may be greater than a predefined value due to some process variables hitting their upper and lower bounds of values in the optimization solution. Based on the process knowledge, the said bounds can be changed and optimization is done with the changed bounds. The optimization results thus obtained can further be analyzed by computing the indices again. k 5 when being greater than a predefined value signifies that the current process or equipment is not operated at the optimal values and that there is a variance of the current operating values of process variables from its corresponding optimal values. Further to this, the variance or offset is reduced enabling the process plant to operate at optimal values and thereby at estimated energy benchmark. The improvements sought through operation can be achieved accordingly by having appropriate control of the process plant through suitable controllers (106) or the like. The invention is further described in specificity to the Basic Oxygen Furnace (BOF) in a steel making plant, as an example, with reference to Fig. 2. The BOF (201) has inputs purporting to hot metal from the blast furnace, oxygen and scrap at its upstream. The outputs at the downstream of the BOF (201) are BOF gas, crude steel and slag. The process variables associated correspondingly with the hot metal from the blast furnace, oxygen, scrap, BOF gas, crude steel and slag are their mass flow rates x x 2 , X3, X4, X5 and xs, respectively.
The objective function (z) herein for the BOF is its cost function and is formulated as follows:
Cost = Upstream energy cost + Downstream energy cost + Utility cost + Electricity cost - Cost of additional energy generated in the process (9)
BOF Cost = (Energy Cost of Producing Material Entering BOF + Energy Cost of producing pure
Oxygen) + (Energy Cost of slag handling + Energy Cost of cleaning BOF Gas) + (Utility
Cost in BOF) + (Electrical Energy Cost for surrounding electrical equipment) - (Equivalent Energy Cost of BOF Gas) (10) z = BOF Cost = (x J C i + x 2 C 2 ) + (x 4 C 4 + x 6 C 6 ) + x 5 C U5 + x 5 C E5 - x 4 C R4 (1 1) Where
Upstream energy cost = Energy Cost of Producing Material Entering BOF + Energy Cost of producing pure Oxygen;
Downstream energy cost = Energy Cost of slag handling + Energy Cost of cleaning BOF Gas; Electricity cost = Electrical Energy Cost for surrounding electrical equipment;
Cost of additional energy generated in the process = Equivalent Energy Cost of BOF Gas; ], x 2 , X 3 , X , 5 , X 6 = Mass Flow rate of hot metal from Blast Furnace, oxygen, scrap, BOF gas, crude steel, slag respectively;
Ci = Energy cost of producing per unit hot metal in Blast Furnace; C 2 = Energy cost of producing per unit oxygen that is fed to BOF;
C 4 = Energy cost of cleaning per unit BOF gas;
C R4 = Energy cost of recoverable energy per unit BOF gas;
Cu5 = Equivalent Energy Cost of utility (steam, water) consumed per unit of output steel production;
C E5 = Electrical Energy Cost consumed per unit of output steel production in BOF; and C 6 = Energy Cost of slag handling
BOF gas can be utilized as a fuel in other furnaces in the plant. The slag is handled in the slag handling unit (202). C R4 is the cost associated with chemical (or thermal) energy in BOF gas and can be calculated using heating value of the gas for a standard composition of BOF gas. It is necessary that the energy values should either be converted to equivalent thermal energy or electrical energy to formulate a cost function for optimization. The optimization will have constraints related to design or operational limitations that should be included in the formulation. Some of these constraints are as follows: Mass balance on BOF, which is written by assuming yield for production of steel from hot metal and scrap. x 5 = Yield * (x l +x 3 ) (12) The capacity constraint on the BOF process is as follows:
In some plants there can be an operational constraint (best practice) that the hot metal and scrap are fed at a minimum ratio of 4: 1. i.e. JC, > 4x 2
There can be additional constraints based on the demand of output steel, constraints on the flux material that are added along with the scrap etc. The optimization criterion is to minimize the cost by manipulating the metal and scrap charge within the specified constraints. The invention not only provides a method and a system for energy benchmarking through optimization on one part but also diagnosis for the gap between the current energy consumption of the process plant and the estimated energy benchmark. Hence the invention provides a solution to address the problem associated with the rightful approach for energy benchmarking for the process plant and diagnosing the gap thereof accordingly. The example and embodiment described herein before in the description is only exemplary and not exhaustive in nature. Certain aspects have not been elaborated and are clearly known for a person skilled in the art. Modifications or variations to any aspect of the invention, though not explicitly stated, are to be construed within the scope of the invention.