2022年10月25日
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MKP ENGINEERING LLC
Eye opening Engineering《No.1》Temperature is delayed⁉
Temperature is delayed⁉
It happened in Thailand on May, 2004.
Gas engine power plant of 16KU30GA(5.1MW) for Kangwal Textile in Thailand.
Ｇas engine named as ＫU30ＧA was newly launched in 2001, which is pilot ignition type using diesel oil.
The first unit was installed in Yokohama Kanazawa works of Mitsubishi Heavy Industries, Ltd and started operation in 2002.
This Thailand plant was the first order for abroad market on December 2002, But this order was the 28th engine from the above launch. This means that New gas engine KU30GA nicknamed as MACH had been sold very well 27 numbers in domestic market from 2001.
In those days from the view point of environment, domestic customers intended to introduce gas engine of less exhausting CO2 than diesel engine. There was incentive from Japanese government for using city gas. As the result of above, new gas engine was sold massively.
After receipt of this order, I became the Project Manager (PM) of this Thailand plant. I took communications with foreign makers, had meetings with customer’s subcontractors of civil and erection works and gave them several instructions about gas engine power plant construction works. I had managed the plant up to the final taking-over operation in 2004.
According to the customer’s information that commissioning test was ready to be started, six members including me for commission test went to the site in Thailand on May, 2004. The five members except me were the pick of each section, specialist for engine, plant, instrument, fabrication, operation respectively.
These picks were selected by an order of the general managers group since the engine was the first unit for abroad plant.
There were several anxieties.
Especially fuel gas was one of them. It was supplied by PTT which is a public petroleum company in Thailand. We had an information that fuel comes form gas well of seabed in Myanmar and its calorie is very low though its methane number is high compared with city gas in Japan.
Low calory means that more fuel gas is required for combustion.
So, gas supply valve, so called ‘SOGAV’, integrated in engine is bigger size than Standard design in this engine. Accordingly, pipe size for gas line is also bigger than usual design. These matters were anxieties.
There was an absorption chiller among auxiliaries in this plant, which was Purchased and supplied by the customer. Primary cooling water of engine was designed to pass into this chiller. We had an anxiety of adjustment of flow balance into chiller and bypass line.
In addition, MACH gas engine was planned to be operated with other small Caterpillar gas engines in parallel.
The initial engine starting was carried out smoothly on May, 24 unexpectedly.
During the commissioning test, operation was stable. Because the methane number of fuel gas was higher than that of Japanese city gas, operation was less nocking and stable ignition.
Regarding the flow balance to the chiller, the adjustment was successfully done by means of line flow meter, though controlling valve opening degree was a little bit hard.
The parallel operation with Caterpillar engines was also successfully carried out.
During the commissioning test, I was very surprised at lots of intake air drain discharged from rear side of air cooler.
I thought the drain amount is higher in Thailand than it in Japan due to high humidity. But the amount was higher than my supposition. I remember it even now.
Proceeding the commissioning test, load test was carried out.
According to load increase, the temperature of primary cooling water become gradually high. At that time, the setting point of primary cooling water at outlet of engine was 90 degree C. In case the temperature reaches the setting point, water is cooled by cooler in which water is led by control of three-way valve. In spite of the cooling function, the temperature continuously increased up to 95 degree C, the alarm was happened.
In general, this phenomenon is called as Overshoot.
By means of the operation of three-way valve, temperature goes up over the setting value until certain up and goes down. Finally, temperature is settled around the setting value. However, in this plant there happened alarms in several times.
In the plant of our Kanazawa works, the temperature control valve for primary cooling water was wax type which setting value was determined by setting of wax condition. But in this Thai plant, because of adoption of heat recovery system, air operated three-way valve was applied so as to react rapidly for change of temperature. It has an advantage of change of setting value freely.
Then I asked to Mr. S who is a young instrument engineer that the setting value of temperature control valve is changeable or not during engine operation.
He replied it is easy to change.
We firstly fixed the setting value at 80℃, and started engine.
The primary cooling water temperature became gradually increase and went up 80℃, overshoot, went down and settled around 80℃, then we changed the setting value to 85℃. The temperature fluctuated in same manner and settled around 85℃, then we changed the setting value to 90℃ finally, and settled around 90℃.
Thus we settled this overshoot alarm problem.
The reason why alarm happened is
- The water volume of primary cooling water line is higher than that of standard design because of existence of absorption chiller.
- This means that heat equivalent is bigger. This results in taking time for change of temperature.
-As a result, it takes time for hunting motion and more overshoot over the alarm setting value. It causes the alarm.
We call this gradual change of setting value as ‘ Step control ‘ and this has been adopted in MACH plant as standard from then.
In traditional diesel plant, as it takes about 50 minutes for uploading from start to 100% load, there doesn’t happen the problem like big overshoot even at 90℃ setting value of primary cooling water temperature.
On the other hand, in case of gas engine, there is an advantage to take load from start to 100% load in around 5 minutes because of good ignition and stable combustion. In case the setting value of primary cooling water temperature is 90℃ same as diesel engine, in accordance with load increase, water temperature increase is delayed, there happens big overshoot and results in problem like above mentioned.
This Step control can settle the problem.
It is essential for design of gas engine plant.
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