Catalytic combustion heater

Details Catalytic combustion heater Catalytic combustion heater

2000-06-23

2002-03-05

Lu, Jiping (Department: 3749)

Liquid heaters and vaporizers

Heat transmitter

C122S00400R, C122S00700A, C122S367300, C165S299000, C165S300000

Reexamination Certificate

active

06352054

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a catalytic combustion heater that heats an object fluid with heat from an oxidation reaction of a fuel gas with a catalyst, and, more particularly, to a catalytic combustion heater that has a short activation time, when the heater is activated.
FIELD OF THE INVENTION
A so-called catalytic combustion heater, which causes an oxidation reaction of a flammable gas (fuel gas) with a catalyst and heats an object fluid using the generated heat, is known, and various applications of the heater, such as home use and vehicular use, have been studied (for example, Japanese Unexamined Patent Publication (KOKAI) No. Hei 5-223201, etc.). A catalytic combustion heater is equipped with a catalyst-carrying heat exchanger having tubes located in a flow passage of a flammable gas and in which an object fluid to be heated which is a liquid or gas flows, with multiple catalyst-carrying fins integrally joined to the outer surfaces of the tubes. The multiple fins carry an oxidation catalyst, such as platinum or palladium. When the catalyst-carrying fins are heated to or above an activation temperature and contact a flammable gas, an oxidation reaction occurs on the surfaces of the fins. The oxidation reaction generates heat, which is transferred from the fins into the tubes to heat the object fluid that flows in the tubes.
The flammable gas is mixed with a combustion support gas (normally, air) for oxidizing the flammable gas, and is then supplied as a fuel gas into the catalyst-carrying heat exchanger. Because the catalyst-oriented oxidation reaction occurs in a very wide range of the flammable gas concentration, unburned gas, which has not reacted at an upstream location can be burned with a catalyst at a downstream location, and combustion can be carried out along the entire heat exchanger. This provides a compact and high-performance heater as compared with burner type heaters, which have been typical so far.
It is desirable to rapidly raise the temperature of fins to quickly make the catalyst of the entire system active when the catalytic combustion heater is activated. Normally, therefore, means for detecting multiple temperatures, such as the fin temperature, the temperature of the object fluid to be heated and the combustion-exhaust-gas temperature, based on a previously prepared map are provided, so that the flow rate of the object fluid is gradually increased to a specified rate while monitoring the temperatures. In the case of heating water of normal temperature to vapor at 300° C., for example, the flow rate of the object fluid is controlled such that the flow rate of the object fluid is set to zero until the fin temperature on the upstream side of a flammable-gas flow passage reaches the activation temperature, and the fin temperature does not fall below the activation temperature thereafter while making sure that the other catalysts become active in order and the activation temperature is maintained.
However, the conventional catalytic combustion heater must monitor multiple temperatures or detect the fin temperature and the temperature of the object fluid at plural locations in the flammable-gas flow passage and requires complicated control procedure. Further, the heater may not start as expected, depending on variations in the initial temperature of the object fluid or the combustion support gas. Furthermore, if the flow rate of the object fluid is not controlled properly, e.g., if the flow rate is too small, the heat generated on the fin surfaces is not transferred away, which heats the fins and tubes locally and deteriorates the catalyst. If the flow rate is too large, on the other hand, the fin temperature is too low and the catalyst reaction does not occur. This leads to the discharge of unburned gas, which deteriorates the exhaust emissions. There is another problem in that it takes too long to activate the heat exchangers.
SUMMARY OF THE INVENTION
The present invention has been devised to overcome the above conventional problems, and it is an object of the present invention to provide a safe and quick-activating catalytic combustion heater that activates quickly with a simple structure while preventing local heating of the fins and the tubes and preventing discharge of unburned gas.
A catalytic combustion heater according to the present invention is equipped with a catalyst-carrying heat exchanger having tubes located in a fuel-gas flow passage, the interiors of which serve as an object fluid flow passage. Fins are joined to outer surfaces of the tubes and carry an oxidation catalyst for causing an oxidation reaction when contacting a fuel gas. An object fluid is heated by oxidation reaction heat of the fuel gas. The heater includes means for detecting the temperature of the object fluid in the vicinity of an outlet of the object fluid flow passage and flow-rate control means for controlling the flow rate of the object fluid when the heater is activated based on the temperature of the object fluid detected by the temperature detecting means. The flow-rate control means maintains a small flow rate of the object fluid until the temperature of the object fluid exceeds a predetermined temperature and increases the flow rate of the object fluid when the temperature of the object fluid exceeds the predetermined temperature.
When heating the object fluid, the amount of heat required to raise the liquid to the boiling point is smaller than the latent heat for converting the liquid to a gas. The way heat is transferred in the tubes varies in accordance with the state of the object fluid. For example, the heat transfer coefficient of an object fluid in a liquid state is lower than that of an object fluid in a boiling state, which is a gas-liquid mixed state. Accordingly, the activation control can be carried out well by detecting the temperature of the object fluid in the vicinity of the outlet of the passage where the object fluid becomes hottest, to find the state of the object fluid, and by controlling the flow rate of the object fluid based on that state. That is, in the initial stage of heating, the flow rate of the object fluid is maintained low to suppress heat transfer to the object fluid, thereby quickly raising the temperatures of the fins and tubes to the activation temperature. When the temperature of the object fluid exceeds a predetermined temperature, e.g., the boiling point, the flow rate of the object fluid is increased to increase the flow speed, which increases the heat transfer to the object fluid. This prevents the temperatures of the fins and tubes from becoming too high. In this manner, the generated heat can be used effectively to make the entire heater activate quickly. Therefore, the heater can provide the desired high temperature gas in a short activation time, has a simple structure, need not monitor multiple temperatures, and is very safe.
In one embodiment, the flow-rate control means performs control to set the flow rate of the object fluid to a low rate, when the heater is activated, so that the flow of the object fluid becomes laminar, maintains that flow rate until a typical boiling point of the object fluid is exceeded, and increases the flow rate of the object fluid to a specified rate when the temperature of the object fluid exceeds the typical boiling point.
Specifically, the flow rate of the object fluid is controlled based on the boiling point of the temperature of the object fluid, and the flow rate of the object fluid is kept low to make the flow speed sufficiently low. Particularly, if the flow of the object fluid is kept laminar, the heat resistance is increased, making heat transfer in the tubes difficult. Accordingly, the temperatures of the fins and tubes increase, thus ensuring quick activation. Since the quantity of the object fluid is small, it boils relatively quickly. Because the heat resistance abruptly decreases in the boiling state, and heat transfer becomes easier, the vaporization of the object fluid is increased while the flow rate is small. When all of the object fluid is vaporiz

Affiliated with

Also associated with

Rating

Catalytic combustion heater does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Catalytic combustion heater, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Catalytic combustion heater will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2876336