The Energy Management System (EMS) package for Energy and Process industries can reduce the energy cost of a plant by 2 to 4%. With increasing global competition, lowering the costs of plant operations is an imperative for survival.
The energy management problem is a complex one with power purchase, produce power and sell power. It also uses multiple fuels, some of which are by-products of the process plant.
The EMS can monitor the plant and furnish load, steam and fuel allocation including the amount of power to be bought from the grid. If there are options on the consumption side between electrical and steam driven drives, this is also embedded in the EMS.
The system does the following:
• Monitor plant electrical and other energy parameters.
• Predict future energy demands based on current parameters and future production schedules.
• Predict in-house availability of fuel/fuels based on current parameters and future production schedules.
• Generate long term (24/8 hours), medium term (1 hour) and short term (5 mins) schedules.
• Generate the necessary schedules for fuel, steam and electrical load allocations for the individual turbines, boilers, and other equipment (e.g. options at drive level if such options are available).
• Suggest load shedding strategies consistent with plant safety and economic operations of the plant in case enough energy/steam is not available.
• Schedule coke oven battery operations to synchronise with overall plant energy needs and economy.
The online energy management system gets plant data continuously from the various systems installed in the plant. It uses predicted schedules and online data to do the following:
a) Produce a 24 hour ahead schedule for the plant.
b) An hourly schedule which corrects the 24 hour schedule for major changes in input parameters as well as future demands.
c) Every 5 minutes adjusting of the set points of the plant as a decision support to the operator.
This online energy management system therefore continuously uses the plant data to not only produce the day ahead schedules or day shift schedules but also allows the operator continuous support for minimization of energy costs of the plant subject to meeting steam and electrical demands of the plant.
Energy Modelling and Scheduling: The objective of the system is to achieve reduction in the specific energy consumption by maximising the usage of in-house energy and minimising the purchased energy content. The EMS will monitor the energy items used in the plant and provide guidance for optimally allocating them amongst the different production shops. A number of energy parameters will be monitored by the system including in-house energy items such as Coke Oven gas, Blast Furnace gas, LD gas, steam, oxygen, etc. and bought-out items such as coal (coking and steam), petro-fuels, liquid oxygen etc. The EMS will monitor the current system parameters and provide energy demand predictions based on these parameters using energy models and predictive algorithms. The predictions will be utilised by the operators to generate an appropriate schedule and take operating decisions.
For the purpose of successful implementation, it is important that the area-wise data is collected and brought over to a central location for the energy management system through a Plant-wide Network system. This data is continuously stored and updated in an online database and the energy management software package uses this data continuously in order to produce the decision support for the operator. The methodology used by this package is a Mixed Integer Linear Programming (MILP) approach which can provide the global minimum in terms of energy costs. It might be noted that other approaches such as heuristics do not provide a global minimum but only a local minimum. However, a mathematical programming approach produces a global minimum would always be superior than using such heuristics. The MILP approach also takes into account all possible combination of equipment including start-up and shut-down to provide a long term schedule and continuously evaluates any change in either demand or availability to suggest modified schedules.
The Energy Management System provides the different load shedding schedules to the control system under different conditions. However, the actual load shedding is always carried by “triggers” within the DCS system.