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Abstract

Content

Introduction

Modern boiler plant is a complex structure that includes a variety of equipment related to the whole general technological scheme, the main element is the boiler unit. That boiler unit is designed to produce the required amount of final product (steam or hot water) with specified parameters of quality that the consumer needs.

The energy source for boiler units for various purposes are natural and synthetic fuels in solid, liquid and gaseous states, the heat of the outgoing gas processing units, the heat of exothermic reactions,released in separate processes, etc. In this article we consider the steam barrel boiler is equipped with a gas furnace.

The effectiveness of furnaces of all types is primarily determined by the effectiveness of the combustion process. The effectiveness of the combustion process, in turn, is provided by maintaining the required level of attitude "fuel-air". In this way predetermined that the primary role in the management of furnace fuel device of the automatic fuel control and pressure of air blowing.

For maintaining the required level of attitude "fuel-air" is necessary to measure the amount of oxygen in waste gases, so that is why stationary gas analyzer used.

It must be added that the the effectiveness of boiler unit in general determined by the parameters of quality of the final product, which in this case is a steam. Heat output of the furnace is the control action for the steam-generation system. Therefore, to maintain the steam pressure at the specified level must be appropriate adaptation settings of fuel delivery controller. The necessity of such connection is indicated in many literary sources. However, because of nature of boiler manufacturing and installation such connection is practically never used. Each of these control systems operate independently,responding only to external and internal factors. Communication between them is only through the heating process, and one-way – from the furnace to the barrel. Clearly, this leads to a significant reduction in the effectiveness of main technological parameters of SAR steam-generating system, and sometimes to reduce the efficiency of both the boiler and users equipment.

With that said, the purpose of this paper is to provide effectiveness reliability and safety of the steam boiler through automatic control of the main technological parameters of the flue gas unit, which provides effectiveness of the combustion process and takes into account modes and the dynamic properties of steam-generating system in the form of appropriate correction ties.

1. The purpose and principle of operation the boiler plant

As a fuel for boiler plants used coal, peat, oil shale, wood waste, gas and fuel oil. Gas and oil – effective sources of heat. In their use the design and layout of the boiler units simplified, their efficiency increasing and operating costs reducing .

The main elements of the boiler plant are:

- boilers filled with water and heated by fuel burning;

- furnaces where fuel is burned and get heated to high temperature waste gases;

- flues through which flue gases are moving and contacting with the walls of the boiler, give its warmth;

- chimneys, by which flue gases move through the gas duct, and then removed into atmosphere.

Auxiliary the boiler plant elements include:

- fuel delivery and pulverizing devices;

- ash collectors, used for burning solid fuels, and intended for cleaning flue gases and improve the condition of atmospheric air near the boiler plant;

- blowing fans, needed to feed air into the furnace of boilers;

- smoke exhausters, fans that increase thrust and reduce the size of the chimney;

- nutrient devices (pumps) required for water delivery in boilers;

- devices for feed water to prevent scale formation in boilers and corrosion;

- water economizer, used to preheat feed water before it enters the boiler;

- air heater, designed to heat the air before it enters the furnace by hot gases leaving boiler;

- thermal control devices and automation equipment that provide normal and smooth operation of all parts of the boiler plant.

Picture 1.1 – Boiler plant scheme

Picrture 1.1 shows the scheme of the district heating boiler plant with a boiler (2). The boilers can run on liquid and gaseous fuels, so they are equipped with torches and nozzles (6). The air required for combustion is supplied to the furnace by blower fans (5), driven by electric motors.

Water is pumped into the boiler (4), driven by electric motors. After passing through the heating surface, the water is heated and goes to consumers, where gives some of the heat, and with reduced temperature returns to the boiler. Flue gases are removed from the boiler into the atmosphere through a pipe (1).

This boiler has a semi-open layout: the lower part of the boilers (up to a height of 6 m) located in the building, and the upper part of them – in the open air. There are blower fans, pumps and control panel Inside the oiler plant. On the ceiling of the boiler plant installed deaerator (3) to remove oxygen and carbon dioxide from the water.

According to ongoing transformation processes distinguish heating ,evaporating and steam-overheating heating surface. Warmth from the combustion products can be transferred by radiation or by convection. According to this distinction is made between the heating surfaces:

Radiation heating surface receives warmth from gas is mainly due to their radiation. Much of this surface, which is located in the furnace, called a shield. Depending on the location shields are divided into side (pipes located on the side walls of furnaces), front (pipes are on the front wall), etc.

 Convective heating surface receives warmth from gases on contact (convection) with them. It is located in the gas flues of the boiler where heat transfer by radiation not the main , and in magnitude considerably less than the transfer of heat by convection.

Picture 1.2 – boiler functional scheme

1 – Feed water pump, 2 – Economizer, 3 – cylinder, 4 – steam-overheater, 5 – steam-cooler 6 – evaporation elements, 7 – blow fan, 8 – spreader, 9 – furnace, 10 – air heater, 11 – smoke exhauster.

Despite on wide variations in the device for all boilers in fact proceed two identical main processes: combustion of fuel gas with the formation of high temperature (combustion) and the transfer of heat from these gases to water.

2. Goal and tasks of the research

Heat production is always a very important problem of modern life, and the modernization and improvement of this process is always relevant. At the moment most of the boilers in dire need of modernization, since they are practically not automated and a majority of processes managed by a person manually, avoiding mistakes.

As a rule, on the majority of boiler plants, most of the regulatory boiler parameters still work in manual mode, what leads to serious environmental pollution and inefficient use of fuel in the modes of surplus or deficit air for combustion.

The purpose of this paper is to analyze the technological parameters of the gas furnace unit for further automation. Need to increase the efficiency of flue gas control device by taking into account the composition of waste gases and heat load.

The paper identified the following objectives:

1) analysis of the individual subsystems of the gas boiler as local objects of automatic control;

2) synthesis system of automatic control of technological parameters of the flue gas devices;

3) analysis of the stability of automatic control systems to changes in thermal load and the parameters of combustion.

3. Analysis of existing systems of air supply mechanisms in boiler plant 

Automated system of air supply mechanisms is designed for performance management of blowing fan and smoke exhauster of the boiler, using frequency converters in accordance with the technological regulations and modeline map and for effective combustion and saving fuel in thermal power and steam generation heat supply and provide consumers with hot water, save energy, improve equipment reliability, informing staff about the course of the process.

Automated System performs the following functions:

- collection, processing of analog and digital signals;

- control of process parameters: a rarefaction in the furnace and the combustion air pressure depending on the gas pressure (in accordance with modeline map – the ratio of the gas-air);

- automatic and remote control of executive mechanisms;

- control of technological processes in real time;

- testing and self monitoring equipment;

- protection against the destruction of software and unauthorized access to information;

- protection of electric motors driven by emergency modes of operation (overload, phase loss, low and high voltage coupling breakage, etc.);

- automatic reclosing draft machines in the mode of ventilation of the boiler with the disappearance and subsequent reduction of system voltage power supply;

- formation of a warning signal in error situations

The purpose of creation and implementation of an automated system is to achieve optimal production and economic, technological and technical parameters of the boilers through the introduction of modern technologies and advanced management.

Reaching the main goal is provided by:

- improving the accuracy of controlling the parameters of the process;

- high efficiency of process control;

- the expansion of information and control system functions;

- provision of sufficient, reliable and timely information about the process and status of equipment for operational management by personnel;

- increasing the productivity of maintenance staff;

- decrease the influence of human factors on the production process;

- savings in electricity consumption (on average 35%);

- a small saving of gas consumed.

The objects of control and automated management system are:

- air supply system for combustion;

- the regulatory system of rarefaction in furnace.

Conclusion

Heat production is always a very important problem of modern life, and the modernization and improvement of this process is always relevant. At the moment most of the boilers in dire need of modernization, since they are practically not automated and a majority of processes managed by a person manually, avoiding mistakes.

One of the main problems in the boiler plants, in economic and environmental issues, is the fact that do not regulated power of smoke exhausters and blow fans. The engines all the time working at maximum capacity, and the operator controls the boiler air supplying and waste gas exhausting manually opens or closes the gate. Due to a management system engines, wear faster, harmful emissions goes into the atmosphere because of lack of air or loss of efficiency due to the excess air. The ideal ratio for the combustion air / gas – 1/10, but actually use 1/8-1/7, and because of manual configuration can be brought down to the 1/3, what leads to high fuel losses and to increase the content of harmful gas emissions .

Creating an automatic control system fuel and air supply into boiler furnace substantially will reduce costs and harmful emissions into atmosphere. By measuring the amount of oxygen in waste gases and taking into account thermal load at a particular time, you can effectively control fuel and air supply to maximize efficiency.

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