The project was to convert the control of three boiler feed water pumps to Variable Voltage Variable Frequency (VVVF) drives having a capacity of 750 m3/H @ 220 Kg/Cm2 pressure and power rating of 6200 KW each.
The main focus of this report is the design and development of the protection system, sequence of operation, bypass system, speed control system, drum level control and graphic interface. It also includes PID controller tuning for VVVF drive smooth control.
Table of Contents
Executive Summary:
Introduction:
Background:
Responsibilities & Challenges:
Planning
Hardware Planning:
Software Planning:
Execution:
Sequential Logic Development
Mode Selection:
VVVF Drive ON/OFF Commands:
BFP minimum flow protection:
Sequence System:
Control Logic Development
Boiler Drum Volume:
Boiler Drum Hold up Time:
Unit Run Back Logic:
Boiler Drum Water Consumption Rate:
Drum Level Controller Calculations:
Boiler Drum Level Adaptive Control:
Standby Drum Level Control:
DCS Self-sustainability:
Simulation & Commissioning:
Results & Achievements:
Project Objectives and Focus
The primary objective of this project was to implement Variable Voltage Variable Frequency (VVVF) drives on boiler feed water pumps to reduce the plant's auxiliary electrical load. The research focuses on the autonomous design, development, and commissioning of control systems to maintain stable drum levels while optimizing energy consumption.
- Design and development of a custom VVVF drive control system without OEM support.
- Implementation of adaptive control logic for precise boiler drum level regulation.
- Development of a robust protection, sequence, and bypass logic for pump operations.
- Achieving significant reduction in unit auxiliary power consumption at varying load demands.
Excerpt from the Book
BFP Minimum Flow Protection:
Operation of centrifugal pumps below their minimum flow requirements is the primary cause of premature pump failure. Hydraulic instability occurs at low flows, causing cavitation, surging, and excessive vibration in the pump.
There was no information available for the required minimum flow at various speeds from the OEM. We only had data of the flow at full speed from minimum flow line which was 247 T/H. The minimum flow protection was on 171 T/H at full speed (50Hz).
Following formulas were used to calculate the flow curve and pressure with respect to frequency / speed of the pump. By using MS excel, graphs were drawn to set the minimum flow line at 05 T/H less than actual. The line head pressure and Dearater pressure were also compensated for minimum flow line that is connected to the Dearater tank.
Summary of Chapters
Executive Summary: Provides an overview of the technical report detailing the planning and commissioning of VVVF drives at the Lalpir Power Limited plant.
Introduction: Outlines the background of the power plant, the existing feed water system, and the motivation for shifting to VVVF drives.
Planning: Details the hardware procurement and software structural planning required to integrate the new drives with the existing DCS.
Execution: Describes the development of sequential and control logic, including mode selection, protection, and the adaptive drum level control strategy.
DCS Self-sustainability: Explains the design measures taken to ensure that the control system can operate reliably even in the event of communication failures between DCS subsystems.
Simulation & Commissioning: Outlines the rigorous testing procedures and simulation methods used to validate the new control logic before full integration.
Results & Achievements: Presents the project outcomes, confirming smooth system operation and the achievement of significant auxiliary load reduction.
Keywords
Variable Frequency Drives, VVVF, Boiler Feed Water Pumps, Drum Level Control, Adaptive Control, Lalpir Power Limited, DCS, PID Controller, Unit Auxiliary Load, Process Control, Logic Development, Energy Efficiency, Commissioning, Power Plant, Automation
Frequently Asked Questions
What is the primary goal of this project?
The main goal was to install VVVF drives on boiler feed water pumps to reduce the unit's auxiliary electrical load and improve control efficiency.
What are the central thematic fields covered in this report?
The report covers control system design, pump protection, sequence logic development, and the implementation of adaptive control loops.
What is the core research question addressed by the author?
The author investigates whether an in-house developed control strategy can successfully regulate boiler drum levels using VVVF drives without reliance on Original Equipment Manufacturer (OEM) support.
Which scientific or technical methods were applied?
The team used process behavior analysis, Ziegler-Nichols closed-loop tuning, and adaptive control algorithm design based on mathematical calculations of drum volume and consumption rates.
What is covered in the main section of the report?
The main body focuses on the step-by-step logic development for sequential control, protection systems, and the tuning of PID controllers for smooth pump operation.
Which keywords best characterize this work?
The work is characterized by terms such as VVVF drives, Boiler Feed Water, Adaptive Control, DCS, and Unit Auxiliary Load reduction.
Why was it necessary to develop an adaptive control system?
Fixed gain controllers were insufficient because process parameters change significantly between minimum and maximum load points, risking system stability.
How does the unit run-back protection function during a pump failure?
If a pump trips and the standby pump fails to start, the system automatically sheds the unit load to 180 MW to prevent boiler damage due to low drum levels.
What makes this project unique in Pakistan?
It is the first project in the region to utilize adaptive control for this specific capacity of boiler drum level control and to implement automatic pump cut-in/cut-out on frequency control.
- Quote paper
- Tehseen Ahmad (Author), 2015, Implementation of Variable Frequency Drives (VFD) on Boiler Feed Water Pumps for Drum Level Control, Munich, GRIN Verlag, https://www.grin.com/document/298967
