OPTIMIZATION OF COGENT PLANT STEAM SUPPLY INTEGRATED WITH PLC CONTROL SYSTEM IN PT. MNA KUALA TANJUNG

Economic dispatch is often used in general to solve the problem of optimizing the fuel consumption of the electric power system, which focuses on developing optimization methods for a generation system. SCADA/PLC is used so that Economic Dispatch can run in real time on a system. In this research, an automation system will be designed that integrates Economic Dispatch into PLC in a generating system of 3 production boilers operating simultaneously (Cogent System) which aims to ensure that the Economic Dispatch system can run in real time. The simulation results show that the Economic Dispatch program on the PLC can run well. In the simulation of a steam load of 76 MT, the optimal value for boiler 1 is 45 MT and for boiler 3 it is 31 MT while in boiler 2 it is 0 MT, with the opportunity to save boiler fuel use by 16.8% and steam production cost can be reduced by 10% from its initial value.


INTRODUCTION
Fossil energy is a non-renewable natural resource. Oil, gas and coal mining activities will continue to reduce the availability of these resources (Ir. Wijono Ph.D., Dheo Kristianto., Hadi Suyono, ST., MT., Ph.D 2014). In the end, this condition will lead to an energy crisis which will certainly have an impact on the ability of the economic system to produce products and services and can also increase the cost of energy itself (Kanata 2017). The increase in energy costs in the components of production costs in industry will certainly cause its own problems for companies.
In an effort to prevent this energy crisis, the world has taken anticipatory steps by making several policies(Martha Dewa 2016). One example is the issuance of a standard system that regulates energy  PT. MNA Kuala Tanjung is a company engaged in manufacturing palm oil processing. The company has also implemented ISO 50001 since 2012. In its operation process, the company uses a variety of energy according to the needs of existing equipment. Steam (thermal) and electrical energy are the most significant types of energy use. In 2018 steam energy was used for 76.5% of the total energy used, while electricity was in second place with 20.3% of the total energy. Other energy used, such as fuel oil and biogas, is used only by 3.2%. Calculation of economic operations or Economic Dispatch with iteration method using a computer. This is because the computer is able to speed up the iteration calculation process compared to manual calculations, but the use of Economic Dispatch is limited to research, so that to implement it in a process control system, the role of an operator is needed(Aruan, Siregar, and Sitepu 2013)(P. Marpaung dkk 2017).

A. Economical Operation of Power System Economic
Economic dispatch is very important for the power system to get a return on invested funds. For this reason, efficiency in reducing consumer energy costs and power generation costs is very important.
Economic management includes power generation and transmission, which can be divided into two parts.
One of them is related to the minimum production cost, which is called Economic Dispatch, and the other is related to the loss of power transmission transmitted to the load(Abidin, Robandi, and Wibowo 2012) (Brännlund et al. 2012).
Economical operation aims to reduce fuel consumption or operating costs by determining the output of each power generation unit under charging system conditions. In a generating unit, the Input-Output characteristics are referred to as a function of fuel consumption or a function of operating costs. thermal power generation unit, the boiler input is fuel and the output is the amount of steam (Syafii and Putri 2018).
The value of the generator fuel consumption can be written as MBtu/hour, the fuel cost ratio can be written as $/hour, and the generator output can be written as PG (Yoshimi, Swarup, and Izui 1993). Then the value will fulfill the following equation:

PGmin ≤ PG ≤ PGmax
(1) The characteristics of the input-output curve are non-linear with the following equation: Where , and are coefficient value of the input-output characteristics. The value of is the value of the fuel consumption of the generating unit without output power(Costanza and Rivadeneira 2015) (Komsiyah 2012).

B. Boiler
The boiler steam boiler or steam generator is a device used to create steam by applying heat energy to water. Although the definition is somewhat flexible, we can say that older steam generators have been called boilers and operate at low to moderate pressures (7-2,000 kPa or 1-290 psi) (Ryashentseva et al. 2015).

Figure 2. Illustration of Boiler -Steam Boiler
Cogent Plant System is the generation of electricity and other energy carried out simultaneously.
Cogent in fuel is the use of fuel to produce heat more efficiently, because otherwise the wasted heat from power plants can be used for productive use. More thermally efficient in fuel use than standard energy production, which only produces unusable process heat, cogeneration makes better use of the heat energy generated in addition to the electricity generated.

C. PLC (Programmable Logic Controller)
A programmable logic controller (PLC) is simply a special computer device used in industrial control systems. It is used in many industries such as oil refineries, production lines and transportation systems.
Whenever you need to control a device, PLCs provide a flexible way of "software linking" components (Almuhtarom and Sasmoko 2015). This research uses PLC GE Versamax Micro IC200UDR005 and HMI Simplity in Figure 3.   In distribution, the steam load is divided into 2 systems, namely the 13 bar system and the 3 bar system. A PRV is used which serves to lower the steam pressure level to the desired level so that both systems can be met, at the same time this PRV can also regulate the amount of steam flow to the load. And the next step is to make a design scheme implementation of research that is integrated into the PLC. Figure 5 is an Economic Dispatch design for the Steam boiler system Tools and materials used in this study are described in table 1 as follows:

Sampling Locations And Points
The research location was conducted by PT. Multimas Nabati Asahan with the address: Access Road Inalum, Kuala Tanjung village, Batubara Regency. With a sample of bio-mass fuel in the form of palm shells and steam production for each boiler during the period July 1, 2017 to June 30, 2018

Method
The method used in this study uses the lambda iteration method to calculate the value of fuel savings and operational cost savings and integrates the PLC programming language and then simulates it into the HMI Software.

Data analysis
Data analysis was carried out using the Ms. application. Excel to get the results of the lambda method of 3 fuel usage from the boiler. And simulate in graphical form to get the values of y1, y2, and y3 on the boiler

A. Results of Fuel Data and Production Data
Results of fuel data and production data after ratio analysis and data cutting which is not active in the three boilers and is re-tested after cutting the correct data seen in

B. Formulation of boiler input-output curve
To obtain efficiency values and curves for boilers in table 1 It can be described in the form of inputoutput curve in Figure 6 : Based on Figure 6, it is also found that the R2 values for y1, y2 and y3 respectively are 0.970, 0.962 and 0.963, where this value shows the equation of each input-output curve is valid.

C. Economic Dispatch dalam PLC
Integrate Economic Dispatch formula in PLC system. PLC is divided into 2 types of programs, namely PLC programming and HMI programming. PLC programming, the programming technique chosen is to use a ladder diagram. Figure 7 is a form of ladder diagram programming on a PLC  HMI programming used for this research is a control system of a process for controlling the boiler output flow. HMI programming on this boiler system is shown in Figure 8.

D. Analysis of Fuel Use
Analysis is carried out by comparing the actual value with the calculated value of Economic The Dispatch analysis carried out took data from the last 12 months in tabel 3.  The explanation of table 3 shows the total fuel cost for the three boilers is Rp. 46,697,300,000,-down to Rp. 38,828,880,976, -so the chance of saving is Rp. 7,868,419,024,-. In terms of the cost of steam production, there is also a decrease in costs in terms of fuel costs. The fuel cost based on field data is 100% per MT of steam. After optimization, the fuel cost fell to 90% per MT