JPH09316608A - Rotary regeneration type heat exchanger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide new heat transfer elements which are capable of sufficiently withstanding the corrosion by moisture condensation, are inexpensive and are free from the worry about crack. SOLUTION: This rotary regeneration type heat exchanger preheats air A1 for combustion by using the heat transfer elements 2c loaded in a rotor 2b as heat accumulation bodies and bringing a high-temp. combustion gas G1 and the low-temp. air A1 for combustion into alternate contact with each other to transfer the heat of the combustion gas G1 to the air A1 for combustion. The heat transfer elements 2c consist of a 7% Cr steel of low C and low Si.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a heat transfer element loaded in a rotor as a heat storage body to alternately contact a high temperature combustion gas and a low temperature combustion air to heat the combustion gas into the combustion air. The present invention relates to a rotary regeneration heat exchanger for transmitting and preheating the combustion air.

[0002]

2. Description of the Related Art Generally, a rotary regenerative heat exchanger used in a thermal power plant supplies preheated combustion air to a boiler using petroleum-based fuel, coal-based fuel or LNG (liquefied natural gas) fuel. First, the heat of the high-temperature combustion gas from the boiler is temporarily stored in the heat transfer element, and is transferred to the combustion air as the rotor rotates, so that the combustion air is preheated.

In the conventional rotary regenerative heat exchanger, in the case of a boiler of petroleum or coal fuel containing sulfur,
In particular, sulfuric acid condensation occurs in the heat transfer element on the low temperature side, and the heat transfer element is corroded. On the other hand, in a LNG fuel system boiler that does not contain sulfur, the heat transfer element undergoes so-called water corrosion due to the condensation of water in the combustion gas. A heat transfer element that has been corroded has problems such as a decrease in heat transfer efficiency and a shortened life.

The heat transfer element which is corroded by the sulfuric acid condensation is a low alloy corrosion resistant steel (CRLS: Corrosion Resistant) to which a trace amount of Cu or Cr is added.
The above problems are solved by manufacturing using a low alloy steel plate.

[0005]

SUMMARY OF THE INVENTION However, LNG
The heat transfer element of the rotary regenerative heat exchanger in the fuel boiler is not sufficiently solved by the steel plate of the low alloy corrosion-resistant steel, and the existing enamel-coated steel and stainless steel are worried about end face cracking and the cost is high. For this reason, there has been a demand for the development of a new heat transfer element that is sufficiently resistant to corrosion due to water condensation and is inexpensive and free from the risk of cracking.

[0006]

The present invention has been made in order to meet the above demand. The rotary regenerative heat exchanger of the present invention uses the heat transfer element loaded in the rotor as a heat storage body to alternately contact the high-temperature combustion gas and the low-temperature combustion air, thereby converting the heat of the combustion gas into the combustion air. A rotary regenerative heat exchanger that transfers and preheats the combustion air, characterized in that the heat transfer element is made of low C-low Si-7% Cr steel.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 is an LNG-fired boiler of a thermal power plant, the combustion gas G1 of which is sent to a rotary regeneration heat exchanger 2 to lower the temperature. The combustion gas G2 having a low temperature is sent from the rotary regeneration heat exchanger 2 to the chimney 3 and released into the atmosphere. On the other hand, the combustion air A1 is preheated by the rotary regeneration heat exchanger 2 and supplied to the LNG-fired boiler 1 as preheated air A2.

As shown schematically in FIG. 2, the rotary regenerative heat exchanger 2 has a rotor 2b which rotates at a predetermined speed around a rotary shaft 2a, and a heat transfer element 2c loaded in the rotor 2b. Etc. 2d is a rotor housing and 2e is a sector plate. In this embodiment, the lower part of the rotor 2b is on the low temperature side and the upper part is on the high temperature side.

The rotary regenerative heat exchanger 2 having the above-described structure uses the heat transfer element 2c loaded in the rotor 2b as a heat storage body.
By alternately contacting the high temperature combustion gas G1 and the low temperature combustion air A1, the heat of the combustion gas G1 is transferred to the combustion air A1.
1 to supply it to the LNG-fired boiler 1 as preheated air A2.

FIG. 3 shows the heat transfer element 2c,
It is composed of a flat surface portion 2c 'and a double undulate portion 2c ". The shape of the heat transfer element 2c is not limited to this.

The material of the heat transfer element 2c which can sufficiently withstand the corrosion due to the water condensation was developed through the following preliminary experiments and the actual exposure test with the test heat transfer element.

Preliminary Experiment A dry and wet repeated precorrosion experiment in which a gas having a composition close to that of the combustion exhaust gas was aerated was continued in the laboratory, and the results were analyzed. (1) Low CP-Cu-Ni system (2) Low C-5% Cr (3) Low C-7% Cr

However, in the above preliminary experiment, the low CP-
The Cu-Ni system was good in the lab test, but in the actual machine exposure test with the test piece, no significant difference from the conventional product was observed, and the next actual machine exposure test with the heat transfer element for test was not carried out.

Exposure test on actual machine by heat transfer element for test A heat transfer element for test, which was crimped in a waveform, was manufactured and mounted on an actual machine to examine the corrosion resistance performance.
The conditions of the actual machine exposure test were as follows. Venue: Kanto area thermal power plant Plant name: Power generation plant Boiler air preheater Period: May 1994-May 1995 (about 1 year) Air preheater model: 34-HX-2200 Heat transfer element model: FNC Test heat transfer element: Width 200 x Height 300 x Thickness 1.0 to 1.1 mm (1) Low C-5% Cr (2) Low C-7% Cr (3) Control (conventional product) CRLS (Low) Alloy corrosion resistant steel) Initial weight of heat transfer element for testing: 480-530g
/ Sheet (difference due to cutting position and specific gravity of steel type) n: 3

Test Results Corrosion of the heat transfer element appears as an increase in weight due to metal oxidation in the initial stage, but after a few months, the corroded portion is damaged due to vibration associated with the rotational movement of the rotor, resulting in weight loss. Appears as a decrease in As a test result, the corrosion weight loss is shown in FIG. Since the corrosion area due to so-called “water corrosion” is only within a range from the low temperature end to about 100 mm within the height of 300 mm, the difference from the initial weight of each sheet is defined as the amount of corrosion.

As is clear from FIG. 4, the corrosion weight loss of the 7% Cr system was the smallest. FIG. 5 shows the test results of the amount of adhered rust. Of the adhered rust, peelable floating rust was 5% and 7%.
It was found that each of the% Cr-based materials was small.

As a result of the above comparative corrosion resistance test, carbon (C) is 0.01% by weight, silicon (Si) is 0.05% by weight, manganese (Mn) is 0.3% by weight, and phosphorus (P) is 0%. 0.005% by weight, sulfur (S) 0.003% by weight, and chromium (C
It was found that the steel sheet having r) of 7.0% by weight had the best workability and corrosion resistance.

In particular, the amount of chromium Cr added is 7% by weight.
From the above, it was found that the heat transfer element has a corrosion resistance about twice as high as that of the conventional heat transfer element made of steel plate, and has an effect such as less peelable rust.

[0019]

EFFECTS OF THE INVENTION By using low C-low Si-7% Cr steel as the material for the heat transfer element of the rotary regenerative heat exchanger, the corrosion resistance is about twice as high as that of the conventional steel plate heat transfer element. In addition, the effect such as less peelable floating rust was recognized.

[Brief description of drawings]

FIG. 1 is a flowchart of a thermal power plant.

FIG. 2 is a schematic diagram of a rotary regeneration heat exchanger.

FIG. 3 is a perspective view of a heat transfer element.

FIG. 4 is a graph showing test results of corrosion weight loss in an actual machine exposure test.

FIG. 5 is a graph showing test results of weight of deposits in an actual machine exposure test.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 LNG-fired boiler 2 Rotational regeneration type heat exchanger 2a Rotating shaft 2b Rotor 2c Heat transfer element 2c 'Plane part 2c "Double undulate part 2d Rotor housing 2e Sector plate 3 Chimney A1 Combustion air A2 Preheating air G1, G2 Combustion gas

Claims (1)

[Claims] 1. A heat transfer element loaded in a rotor is used as a heat storage body to alternately contact a high temperature combustion gas and a low temperature combustion air to transfer the heat of the combustion gas to the combustion air. In a regenerative heat exchanger for preheating combustion air, the heat transfer element has a low C-low Si-7% C
A rotary regenerative heat exchanger characterized by comprising r steel.