Steam heating is a steam heating system. In urban central heating system, water is used as heating medium. It takes heat away from the heat source in the form of steam and delivers it to users through the heating network. Depending on the pressure of steam itself, the pressure drop per kilometer is about 0. 1 MPa. The steam supply parameters of China thermal power plant are mostly 0.8 ~ 1.3 MPa, and the steam supply distance is generally within 3 ~ 4 kilometers. Steam heating is easy to meet the heat demand of various processes; The specific gravity of steam is small, so it will not produce excessive static pressure in high-rise buildings; The flow velocity in the pipeline is greater than that of water, which is generally 25 ~ 40m/s; The heating system is easy to start quickly; Heat transfer efficiency in heat exchange equipment is high. However, steam loses a lot of heat energy and heat medium in the process of transportation and use. The heat source not only needs a lot of supplementary water, but also has higher requirements for water quality than the heating network.

Energy-saving technology of steam heating pipe network system

The energy-saving technology of steam heating pipe network system is mainly composed of two key products.

1. The invention is suitable for steam boilers in electric power, chemical industry, petroleum, metallurgy, machinery, building materials, transportation, light industry, textiles, rubber and other industrial departments and hotels, hospitals, shopping malls, office buildings and other units, and realizes the recycling of high-temperature condensed water and secondary steam. It is also suitable for steam heating and lithium bromide refrigeration system of central air conditioning.

2. Low-level thermal deaerator is suitable for high-standard deaerator of steam boiler and hot water boiler.

Main technical contents

I. Basic principles

1. The condensate recovery device has five ideas: decontamination device, automatic pressure regulating device, cavitation elimination device, optimal flow pattern of water pump and automatic control. Under the condition of ensuring normal backwater, the pressure of the special valve of the pressure regulating device should be appropriately increased, which is beneficial to the secondary condensation and the recovery of secondary steam in the container; Second, the secondary steam exerts pressure on the water surface to ensure the positive pressure head necessary for the pump to prevent cavitation; The third is to form a closed pressure system to ensure oxygen-free corrosion of equipment and pipelines.

2. The first stage of low-level thermal deaerator forms several "conical water film skirts", which generate strong heat exchange with rising steam, and the deoxygenation is basically completed. In the second stage, the grid and grid waves are filled with oxygen. When the water inlet conditions are poor (low water temperature, high oxygen content and large water level fluctuation), the deaerator still works normally. In the third stage, the water tank is boiled again to remove oxygen.

Second, the key technologies

1, automatic pressure regulating device of condensate recovery device and cavitation elimination device are jointly applied, which effectively solves the world problem of pump cavitation "pump cancer".

2. The low-level thermal deaerator makes full use of the secondary cavitation removal device, effectively solving the world problem of pump cavitation "pump cancer".

Characteristics of steam heating system:

1. Hot water releases heat in the cooling equipment of the system according to its temperature, and the form of hot water will not change. In the cooling equipment of the system, steam condenses into water to release heat, and its form has changed.

2. Because steam has the characteristics of large specific volume and low density, it will not produce great hydrostatic pressure when heating high-rise buildings like hot water heating. In addition, the steam heating system has small thermal inertia, fast heating when supplying steam and fast cooling when stopping steam, which is very suitable for users of intermittent heating.

First, the basic principle of steam heating system

The heating system with steam as heating medium is called steam heating system. Fig. 7- 1 is a schematic diagram of the steam heating system. Water is heated into steam with a certain pressure and temperature in the boiler, and the steam flows into the radiator through the pipeline under the action of its own pressure. After the steam releases heat in the radiator, it becomes condensed water. After passing through the trap, the condensed water returns to the condensed water tank along the condensed water pipeline, and then is pumped to the boiler by the condensed water pump to be heated again to become steam.

The condensate recovery mode of steam heating system should be determined according to the possibility of secondary steam utilization, outdoor terrain and pipeline laying mode, and the following backwater modes can be adopted:

(1) closed full pipe backwater;

(2) Open water tank gravity flow or mechanical backwater;

(3) Residual pressure backwater.

In the steam heating system, steam condenses into condensed water with the same temperature at a constant pressure in the heat dissipation equipment, and the phase state changes. It is generally believed that the steam entering the heat dissipation equipment is saturated steam, and the temperature of the condensed water flowing out of the heat dissipation equipment is the saturated temperature under the condensation pressure, and the superheat of the steam entering and the supercooling of the condensed water are very small and can be ignored. Therefore, it can be considered that the heat released by the condensation of steam in the radiator is equal to the latent heat of vaporization of steam.

Second, the characteristics of steam as a heat medium

Compared with hot water, steam as a heat medium has the following characteristics:

(1) Using steam as heat medium can meet the heat demand of various users with different requirements on pressure and temperature. It can not only meet the needs of indoor heating, but also be used as a heat medium for other heat users.

(2) Steam releases latent heat of vaporization under constant pressure in heat dissipation equipment, and the average temperature of heat medium is the saturation temperature under corresponding pressure. Hot water releases sensible heat through temperature drop in heat dissipation equipment, and the average temperature of heat medium in heat dissipation equipment is generally the average temperature of inlet and outlet water.

Value. Therefore, the heat release of steam heating system per kilogram of heat medium is larger than that of hot water heating system, and the heat transfer temperature difference of heat dissipation equipment is also large. Under the same heat load, steam heating system needs less heat medium mass flow and heat dissipation equipment area than hot water heating system. Therefore, the steam system saves the initial investment of pipes and heat dissipation equipment.

(3) When steam and condensate flow in the pipeline, the state parameters (density and flow rate) change greatly, even accompanied by phase change. The saturated condensate flowing from the heat dissipation equipment passes through the trap and condensate pipeline, and the pressure drops faster than the temperature, so that part of the condensate is re-vaporized to form "secondary steam". These characteristics make the design, calculation and operation management of steam heating system complicated, and the problems of "running, running, dripping and leaking" are prone to occur, and improper handling reduces the economy of steam heating system.

(4) The density of steam is smaller than that of water, so it is suitable for high-rise buildings (especially super high-rise buildings with a height exceeding 160m) as a heating medium, and the radiator at the bottom of the building will not be over-pressured.

(5) The thermal inertia of steam is small, and the temperature rises quickly when steam is supplied, and the temperature drops quickly when steam is stopped.

(6) The power of steam flow comes from its own pressure. Steam pressure is related to temperature. When the pressure changes, the temperature changes little. Therefore, steam heating can not change the temperature of heat medium by qualitative adjustment, but only by intermittent adjustment. Therefore, the indoor temperature of steam heating system users fluctuates greatly, and there is noise when working intermittently, which is easy to produce water hammer phenomenon.

(7) When steam is used as heat medium, the surface temperature of radiator and pipeline is higher than 100℃. When water is used as the heat medium, the average surface temperature of the radiator is lower than 80C most of the time. When steam is used as heat medium, the organic dust on the surface of radiator will affect the indoor air quality. At the same time, it is easy to burn people, and the invalid heat loss is large.

(8) The steam piping system works intermittently. Sometimes there is steam flowing in the steam pipe, and sometimes it is filled with air; Sometimes the condensate pipe is filled with water, and sometimes it enters the air. Pipes (especially condensate pipes) are easy to be oxidized and corroded, and their service life is short.

Because of the above characteristics, the heating system with steam as heating medium is mostly used in industrial buildings and their auxiliary buildings at present, and can also be used in factory office buildings with short heating period and less steam consumption.