Steam efficiency using recycling
Today, due to the high cost of energy supply to provide the product needed by different parts of industrial processes, the need to recycle the energy produced in the factory support industries is inevitable, one of the most important units in most factories is the boiler unit. Which is responsible for providing steam with the desired temperature and pressure for different parts. In this research, the process information of which has been extracted from Razi Dough and Alcohol Factory, the amount of energy wasted in the boiler 1 of the boilers of this factory has been calculated and the amount of energy that can be recycled has been determined.
Due to the limitation in the preheating of the boiler feed water due to the cavitation phenomenon in the feed pumps, the process of mixing the return flows of the process units and raw water has been analyzed and the maximum difference in the achievable temperature has been calculated. Also, the reduction of boiler burner fuel consumption due to preheating of feed water has been determined. The amount of savings resulting from the thermal recovery of Bludan is about 370146072 Rials per year and the maximum temperature difference that can be achieved for preheating is 17, which shows the importance of this system.
As water evaporates in the boiler, solid particles in the boiler water are left and accumulated. Insoluble particles give rise to sludge formation over time, which reduces heat transfer. These particles also increase the formation of foam on the water surface and intensify the infiltration of water into the exhaust vapor.
In order to maintain the amount of sediments and hardness of water soluble in an acceptable size, the boiler water is discharged into the wastewater at regular intervals. This is done by two separate systems.
Lower bloating: often done manually and at regular intervals (several times a day for less than a minute) to drain heavy sludge and sediment from the bottom of the boiler.
Surface blower: Designed to discharge concentrated soluble particles near the water surface. This system is usually continuous and automatic.
Inadequate blowing may lead to the boiler water being transported into the steam as well as the formation of foam and sediment. Excessive blowing is also equivalent to wasting water, energy and chemicals. . The optimal amount of blower is a function of various factors such as the type of boiler, working pressure, the quality of the inlet water and the type of water treatment system. The amount of bleed is usually about 4% to 8% of the water entering the boiler. If the inlet water hardness is high, it can increase up to 10%.
In Razi dough and alcohol factory, where this study has been done, two saturated fire side boilers with saturated steam product are used, taking into account the operating conditions listed in Table 1. In this article, the operating mode of the boiler is 1 full load.
Most of the steam used in process units is returned to the boiler unit after use and used in a condensate tank for reuse. In addition, some raw water is used to compensate for the shortage of boiler feed water. It is added and finally sent to the deaerator tank by two pumps for deoxygenation and from there it is sent to the boilers by feed pumps.
Table 1: Operating conditions
Maximum allowable amount of water solids (PPM)
|Steam production rate
|Water waste temperature|
Boiler surface heat recovery system:
In this design, we first direct the water from the blower to a flash tank to reduce the pressure. The pressure drop in the flash tank causes part of the fluid to evaporate. The steam generated is used to heat the feed water in the deaerator. The remaining water is used by a heat exchanger to heat the raw water.
Figure 1: Thermal recycling system of boiler boilers
For each double boiler
In this equation, F is the amount of hardness of the incoming water, S is the amount of steam produced, B is the amount of hardness of the boiling water and the enthalpy for water at working pressure.
Steam quality and flash tank effect:
Due to its structure, the flash tank causes the water to drop to a pressure of about 9.5 barg and some of it evaporates. I will continue to calculate the steam quality.
This means that as the boiler water pressure drops in the flash tank, it becomes part of the steam water, which contains about 100 kw of energy from 211 kw. This steam is used to heat the feed water in the deaerator. Residual water in the flash tank is used to heat the raw water entering the condensate tank in a heat exchanger. As a result, water enters the condensate tank at a higher temperature and provides higher temperature water to the boilers. Due to the temperature limitations in the dehumidifier, which are described below, we calculate the temperature of the factory condensate mixture and the raw raw water inlet to obtain the temperature of their mixing and also compare it with the actual values recorded.
The process of mixing condensate returned from process units and raw water:
- 70% of condensate tank water is supplied from the return condensate of the units and the remaining 30% is supplied from raw water.
- We consider the condensate hole as a control volume.
- Condensate water temperature is about 110 and raw water temperature is about 20.
- Heat transfer and work is zero. In this equation, the final temperature value of the water mixture in the condensate tank is the inlet water flow to the condensate tank, the inlet water temperature and the total flow rate. The output temperature of the condensate tank has been read from the collector output of the condensate tank pumps for several consecutive days, which has been compared with its theoretical value in Figure 1. Which indicates the proximity of the actual temperature with the theoretical state temperature. The difference between the theoretical and experimental temperatures is due to the change in the ratio of the amount of incoming water to the condensate hole.
Figure 1: Comparison of temperatures recorded at the condensate tank outlet and theoretical temperature
Residual water energy:
.Flash tank energy
.Recycled energy in the heat exchanger
.Maximum recycled energy
. Percentage of recycled energy
Maximum achievable temperature:
The maximum temperature at which water can be heated varies depending on the type of deaerator in the process units. In this case, the deaerator temperature is 103. That is, the working pressure of the de ortor is about 0.2 brag. If the temperature exceeds this value, water evaporates and cavitation occurs in boiler feed pumps. This means that there is a limit to the heating of the dehydrator water. Here we examine the temperature changes of the inlet water to the deaerator by changing the temperature of the heated feed water according to Formula 6:
In this case, it is observed that increasing the temperature of raw water is not too useful because due to the injection of steam into the dehumidifier, the temperature of the feed water will increase slightly and in any case should not exceed 103 and before entering the dehumidifier tank should not exceed 100 Therefore, the maximum temperature that can be achieved using this system is 17.
Table 2: Maximum achievable temperature for feed water
|90||80||70||60||50||40||30||20||Raw inlet temperature to the condensate tank after preheating|
|104||101||98||95||92||89||86||83||The final temperature of the condensate tank after mixing or boiler feed water|
The final temperature of the condensate tank after mixing or boiler feed water
Fuel saving in the burner:
As mentioned, due to the preheating of the boiler feed water, using this burner method to heat the raw inlet water consumes less fuel. The amount of fuel consumption and the cost that is saved according to the 75% efficiency of the burner, 8400 working hours per year and the calorific value of 10000 kcal are as follows:
Annual cost savings
In this regard, the mass flow rate of recycled fuel, recycled thermal energy, burner efficiency and E are the calorific value of the fuel.
Results and discussion:
1.As it has been said, by recycling the boiler heat of the boilers annually in the amount of 370146072 Rials, the cost of consumed gas is saved.
- In the following diagram, assuming that the cost of each cubic meter of gas consumed is 1000 Rials, a comparison of the reduction of the cost of consumed gas in the second half of 2014 if this plan is implemented is discussed.
Figure 2: Comparison of gas consumption costs without and with heat recovery system in Rials in the second half of 2014 US experts warn about methanol-containing disinfectants
The American Toxic Control Centers Association recently warned against the use of hand sanitizers that contain methanol (methyl alcohol), according to Health News.
The US Food and Drug Administration has previously warned that some hand sanitizers are contaminated with methanol.