Industrial steam boiler house - everything is under the control of automation

Automation of the boiler house solves the following tasks:

• automatic start and stop of boiler units;
• regulation of the productivity of boilers according to the needs of the technology;
• control of pumping groups of make-up and circulation circuits;
• water treatment (purification, deaeration);
• management of the heating and hot water supply system of the plant with an assessment of the weather condition;
• monitoring of the state of pumping stations outside the boiler house: wells and water storage tanks, sewage pumping station;
• emergency shutdown and shutdown of faulty systems with indication of the root cause of the accident, activation of signaling devices in case the operating values of the system go beyond the established limits;
• providing operators with timely, complete and reliable information about the status of all systems and mechanisms using the developed visualization tools.

Modern automation of the boiler house implies an integrated approach - the subsystems for monitoring and regulating individual technological processes are combined into a single network with functional group management.

The boiler house automation complex consists of separate units that work autonomously, but are united by a dispatching system and can interact with each other without the participation of an operator.

The main unit of the boiler house, which justifies its name, is the boiler. The plant uses a special steam boiler, which provides process lines with superheated steam, and also prepares the coolant for the primary circuit of heating and hot water systems. The main fuel of the boiler is the waste of the plant's own production - buckwheat husk, which remains after cleaning and processing of grain. The boiler is ignited by natural gas, and then gradually goes completely to the husk. This provides enormous cost savings, but requires a complex automatic control system. This system automatically starts on natural gas and warms up the boiler furnace. Further, the automation gradually feeds an increasing portion of the husk into the furnace, at the same time reducing the gas supply. The husk enters the furnace from the operational bunker with the help of special fans, screws with adjustable rotation speed, and sluice gates. The rotation speed is determined by automatic algorithms and depends on the desired productivity of the boiler. All this time, the steam pressure at the outlet of the boiler is monitored. During the specified time, the gas supply to the boiler furnace is reduced to an acceptable minimum, after which it is completely cut off and the boiler continues to operate on one biofuel. To improve the aerodynamic processes in the furnace and to prevent the occurrence of husks, a recirculation fan is turned on, which returns part of the flue gases to the furnace. High-quality and complete combustion of fuel in the furnace is possible only if a sufficient amount of air is supplied. Part of it is fed along with the husks, but the main part comes from the operation of the purge fan. The system monitors the current productivity of the boiler, which depends on the amount of fuel, and, accordingly, corrects the required amount of air. An excess amount of air leads to excessive costs for its heating in the furnace, i.e. to waste of fuel. And an insufficient amount of air leads to underburning, when the concentration of harmful impurities in the combustion products increases, and soot is deposited on the heating surfaces of the boiler. The optimal amount of air that enters the boiler is determined by the oxygen content in the flue gases using a stationary gas analyzer. This circuit corrects the efficiency of the blow-off fan equipped with a frequency converter. Fresh air is initially heated by steam heaters. This allows you to optimize current processes.

The vacuum in the boiler furnace, which is necessary for the correct movement of flue gases and washing of the heating surfaces, is provided by the necessary operating mode of the smoke exhauster. It also regulates its productivity, and hence the vacuum value, depending on the boiler load (air supply to the furnace) according to the readings of the vacuum sensor.

The use of frequency converters instead of traditional gates or fan guide vanes on the boiler, which operates in shift modes and not always at maximum power, allows significant savings in electricity and has a positive effect on the operation of engines. Payback in one or two seasons.

Considerable attention is paid to the boiler feed system and the quality of water in its drum. The water level in the drum is kept constant and the amount of make-up water can be adjusted according to the current steam flow. This makes it possible to strike a balance between the consumption of steam and the entry of water into the drum before the water level deviates by a significant amount. The quality of the water in the drum and its desalination are regulated by the blowing system. It is necessary to reduce the amount of dissolved salts that remain in the water after part of it has been converted into steam. This is done by automatically replacing salted water with fresh water. For economical operation of the boiler, it is necessary that the strictly necessary amount of hot water is drained and no more. Purging, which in this case was carried out periodically and manually, was replaced by a constant and automated one and is carried out according to the readings of the salinity sensor. This approach significantly optimizes the salinity parameter of the boiler water and thus leads to a significant reduction in the amount of fuel for steam generation, which was previously used to heat fresh water. In addition, less water, which is also a valuable resource, goes down the drain.

Automation of boilers is complicated by the fact that in steam units there are very high speeds of technological processes. It is beyond the power of the operator to monitor them and maintain optimal performance, this obligation is fulfilled by fast automatic algorithms. At all stages of work, the system clearly monitors all the necessary technological parameters and the state of each involved mechanism. In the event of an emergency, the boiler will be put into a safe state and properly shut down. The operator is informed about the reason for the stop using the notification system and the event log. Timely and fully submitted information minimizes downtime, and often can even help to eliminate the problem without stopping the boiler. All this, together with the provision of the main production of the plant with steam of the required parameters, has a positive impact on the productivity of the lines and the income of the enterprise.

An example of atmospheric deaerator automation

Boilers work with prepared water. First, it undergoes chemical treatment in HVO installations, which are equipped with their own automation. Separate plant status signals can be integrated into the supervisory system. Purified water requires the removal of gases dissolved in it, which would otherwise corrode the heating surfaces in the boiler. This is done by an atmospheric deaerator. In it, water boils at a temperature of 102.4 ° C, since it is at this temperature that soluble gases are best released. It is heated by steam that enters the column and the flooded bubbling stage in the tank. An excess pressure of 20 kPa is maintained in the deaerator, which ensures the boiling of water at the required temperature and the water level in the tank.

If it is necessary to lower the temperature of the superheated steam before it is fed into the technology, a reduction-cooling unit is used. The set temperature and steam pressure are maintained there.

Example of automation of a reducing and cooling plant

An important element of the equipment of the boiler house are the pump groups. They circulate water in closed circuits or transport water in the required direction. The system monitors the status of each pump, regulates its productivity in accordance with the pressure settings, turns on the backup pump in case of an unplanned stop of the main pump. It is possible to rotate the main and standby pumps to equalize engine hours. Well pumps pump water into tanks. These tanks are equipped with level sensors, so the current water supply is known at any time.

The heating system provides the entire plant complex with the required parameters of heat carrier. The hydraulic mode is supported by a frequency converter that controls the productivity of the circulation pumps (with main/reserve switching and the possibility of direct pump activation). The water temperature is determined according to the weather-dependent economic schedule. Additionally, the return water temperature is monitored. Hot water supply ensures the availability of heated water for domestic needs. Heating is carried out through steam-water heat exchangers, the required amount of steam in the primary circuit is automatically adjusted according to the readings of temperature sensors on the pipeline to consumers.

An important tool for evaluating the work of a boiler house is the metering device for consumed resources. They allow you to evaluate the effectiveness of a particular solution, the optimal operation of equipment, etc. Gradually, they are also integrated into the overall information system to provide management with generalized data that reflects the operation of the facility as a whole.

Technical solutions

The automatic control system is built according to the classical two-level scheme: local automation of individual installations and a dispatcher's office for managing the facility as a whole. Industrial Ethernet is used as the main communication interface for data exchange.

The tasks that the boiler house automation should perform are functionally grouped into separate control panels: general boiler equipment, steam boiler, deaerator. Pumping stations, which are remote from the boiler building, are connected to the general boiler board using Ethernet. Remote I/O modules are installed in the pump rooms themselves. This structure allows for autonomous operation of individual installations, but within a single data exchange space.

The dispatching system is built on promising, but already familiar web-technologies. Directly into the control panel of the general boiler equipment, the myBox industrial mini-dispatch server is built in, which is connected to the Ethernet line of the boiler room. It processes and archives the data that comes from the PLC and sends the necessary commands to them.

Visualization of technological processes is carried out through a regular web browser and is available from any authorized device within the network. The implementation of dispatching functions on a separate device made it possible to ensure the simultaneous work of all interested employees - operational personnel, instrumentation and control services, service teams, management - without interfering with each other. Depending on the access level of the user, the detailed information required by the user is provided. For example, the operator monitors the work of processes in the boiler house using a mnemonic diagram, the service department conducts a detailed analysis of the operation of the smoke exhauster according to the indicators of sensors and graphs of productivity changes, and the shift supervisor automatically prepares a report on emergency situations during the shift, the amount of resources consumed and steam generation.

Freely programmable WAGO controllers form the basis of local automation. These PLCs have a modular architecture and a large number of different I/O modules, communication devices and elements that perform specific functions. Thus, you can dial the optimal configuration for a specific task. In order to unify, reduce the range of spare parts, the list of modules has been optimized: PFC200 controllers, 16-channel discrete input modules 750-1405 and output 750-1504, counting modules 750-638, 8-channel input modules of unified analog signals 750-496, analog modules output 750-559. Connectors 750-352 are used to communicate with remote pumping stations. All discrete inputs and outputs are additionally protected by intermediate relays: a slight increase in the cost of control panels by an order of magnitude is offset by an increase in the reliability of the system and minimization of the recovery time of the complex in the event of any emergency in electrical circles.

The PFC200 series main controllers have 2 Ethernet ports on board, the default communication protocol is Modbus-TCP. It is possible to activate the OPC-UA server on the PLC. This is in line with the current trend of standardizing machine-to-machine communication.

The CoDeSys programming environment, which has a significant engineering community around the world and a large number of ready-made solutions, contributes to the rapid deployment of the system and simplifies its support throughout the entire period of operation.

All analog sensors are either replaced with new models with a unified 4-20 mA signal or are equipped with signal converters for the same 4-20 mA, as was the case with the installed thermocouples. This contributes both to improving the operation of information channels, since the current signal is insensitive to electrical noise, and to minimizing the types of PLC modules. In addition, this made it possible to avoid laying expensive compensating cables from thermocouples. The end result of unification is cost savings.

To measure the speed of the elevator web when moving the husk between the bunkers, a discrete inductive sensor-relay installed opposite the impeller of the elevator lower shaft was used. Signals from it are fed to the counting module, which counts the number of pulses per unit of time. This is an analogue of the RKS sensors, but with additional diagnostic capabilities for the actual operation of the bucket elevator.

Three-phase MEO electric drives of powerful gate valves for normal and long-term operation require special reversing starters. Modern hybrid reversing starters Schneider Electric Tesys H were installed instead of Soviet FBRs. In addition to the actual task of switching power circuits of the MEO, the starter implements protection against the motor from overload and phase asymmetry.

Considerable attention is paid to the visualization of technological processes and interaction with the operator. Control panels are equipped with 9.7″ Weintek МТ8090XE touch panels. They display all the necessary information, including in the form of graphs and tables, as well as the functions of fine-tuning each mechanism, emergency limits and delays, features of starting and stopping systems. As a backup method for authorized personnel, manual control of any device is available. These panels allow you to control individual systems.

For the general control of the boiler room, an operator's dispatch console is equipped. Accepted decision to use Web Based SCADA (a specialized program for collecting data, their reflection and transmission of commands to local automation) and the conditions in the control room made it possible to install a regular office personal computer on the console. It is connected to the Ethernet network of the boiler room and has access to the myBox server. And already in it all calculations are performed and the necessary data are formed.

MyBox Extreme BEX-ESNM has 2 separate Ethernet ports, RS232/485 port, 16GB flash memory. An NVIDIA TegraTM 3 ARM CortexTM-A9 Quad Core 4x 1.4 GHz processor and 1GB DDR3 RAM provide the system with the computing power it needs. Independent Ethernet ports allow you to separate the technological Industrial Ethernet, which connects local automation systems, from the boiler room network. Thus, the system becomes more resistant to cyber threats. It is possible to install an additional WiFi module or 3G modem in myBox for a backup communication channel.

The dispatching project itself, which the operator sees and which provides the necessary functions of control, management and analytics of the boiler house, is developed in the environment myDesigner. It's free, which, along with an unlimited runtime license, comes bundled with myBox, makes this solution very attractive from a financial point of view. myDesigner belongs to the modern class of software, where functionality is combined with ease of use. It has a convenient vector mnemonic editor with the ability to dynamicize each property of an SVG element, JavaScript as an internal scripting language, the ability to expand with third-party software modules, a built-in visual report editor, and convenient management of data and message archives. This is an advantage for system integrators, as it allows you to quickly implement projects, spending less resources on training engineers and developing solutions.

In the boiler room, the dispatching system performs the following functions:

• visualization of the current state of operation of all installations and systems connected to the system;
• control and adjustment of each mechanism, inserts of the operation of installations;
• archiving of technological parameters and conditions of installations, provision of archival data in the form of graphs, diagrams and tables;
• access to the monitoring system from client devices (computers, laptops, smartphones, tablets) using a web browser without the need to install additional software;
• differentiation of access levels to the dispatching system and functions available to different categories of users;
• registration of events that have occurred;
• automated generation of various reports of the established form in the form of PDF-files adapted for printing.

The interface is made in the progressive style of High Performance HMI, which focuses on the state of the object, and not multi-colored cartoons. The operator must assess the state of all systems at a glance and make the right decision, so the information is provided to him in an already processed, easy-to-read form.