Increase flue gas temperature

1. Heating of process materials； 2. Electric heating ； 3. Heating with heat transfer oil ； 4. Steam heating.

This post was last edited by arpcd on 2016-11-14 at 19:45. Abroad, I saw a company that used the heat from coke oven flue gas for denitrification (exactly within the 320–350°C range mentioned by the original poster); the temperature of the flue gas there was 250°C, which is a similar operating condition. Apart from the fact that the volume of flue gas is smaller than that of the original poster, roughly half of it, around 150,000 I guess. . The answer is simple: heating is carried out “directly” using coke oven gas. For 150,000 cubic meters per hour of flue gas, approximately 1,000 cubic meters per hour of gas is required (the calorific value of coke oven gas is around 4,000 kcal/m3). The burner used is a simple flat-flame burner that is installed directly in the flue; the flue gas after combustion also goes directly into the flue, where it passes through an SCR denitration reactor before reaching a economizer that heats the boiler water. This is the simplest and most cost-effective method, namely using gaseous fuel for direct heating. . Later, the foreigners switched to using natural gas and LPG, with the principle of using whichever is cheaper.

Could we consider simply destroying the economizer, or using electric heating instead?

The coke oven gas supply is unstable, with a low calorific value.

This post was last edited by arpcd on 2016-11-14 at 22:53. For 300,000 cubic meters of flue gas and a temperature increase of 80°C, even if the efficiency of the heater is 100%, the power required for the electric heater would be approximately 7,000 kW. . . 0.5 yuan per kilowatt-hour; 3,500 yuan for hourly consumption; 8,000 hours per year, resulting in 28 million yuan. . . . . Using natural gas (heat value ~8400 kcal/m3), with a gas consumption of ~720 m3/h and a unit price of 3 yuan/m3, the hourly cost amounts to only 2160 yuan, which is still lower than the electricity cost. When it comes to cost analysis, economic considerations often determine the choice of process to be used.

This post was last edited by arpcd on 2016-11-14 23:07. The question is: are there any cheaper heat sources besides coke oven gas? If it is available, then of course it can be used. If heating the flue gas to 320°C is a requirement for environmental protection purposes in order to achieve denitrification, then there is no other choice but to use coke oven gas. If its stability is an issue, then measures must be taken to ensure stability, unless the cost of achieving such stability exceeds the cost of using other heat sources. Back then, I conducted technical exchanges with foreigners abroad; after passing through the SCR reactor, there was a temperature drop of around 10–15°C. The temperature of the flue gas before treatment was around 310°C, while that of the original flue gas was 250°C. If a GGH is used, heat can be exchanged between the flue gas that has been treated by SCR (at 310°C) and the original flue gas (at 250°C), with a temperature difference of around 10°C maintained. In this way, the temperature of the original flue gas rises from 250°C to 300°C, while the temperature of the treated flue gas drops from 310°C to 260°C before leaving the system. Thus, only about 10°C of temperature increase is needed for the natural gas to raise the temperature of the original flue gas, resulting in very low energy consumption. The foreigners were silent; later, the translator told me that they stopped responding to me. . . . :Lol, after comparing energy prices, I finally understood why the foreigners ignored me – the price of coke oven gas for them is 7 cents per m3; with a consumption of 1000 cubic meters per hour, the cost is only 70 dollars per hour, which amounts to 560,000 dollars per year. Perhaps this amount is even lower than the maintenance costs of a GGH. Plus, there’s the heat recovered by the economizer, so considering all these factors, the foreigners opted to use coke oven gas for heating instead of a GGH. When they saw me doing the cost calculations, they realized I wasn’t easy to fool, so they stopped paying attention to me. . . :lol

That’s indeed the case; sometimes, although the initial investment is higher, the operating costs are lower, which has a significant impact on the return on capital.

The OP has decided on the denitration process; I’ve seen some manufacturers use a denitration method at temperatures over 200 degrees, without the need to heat the flue gas first before carrying out denitration

This post was last edited by arpcd on 2016-11-15 at 15:46. Low- and medium-temperature denitration is, basically, nonsense both in China and abroad; it has nothing to do with proper processing techniques. The main issue is that the lifespan of the catalysts is insufficient – hardly any manufacturer can guarantee that their catalysts will last more than 8,000 hours. It’s not comparable to high-temperature SCR catalysts. . For high-temperature SCR catalysts, if a bidding process is conducted, any manufacturer that does not dare to specify a service life of 24,000 hours would likely feel too embarrassed to participate in the bidding.