Optimization and Experimentation of Modified Throttling Calorimeter

Steam plays a vital role in the industrial revolution and is a major source of power generation in steam engines or steam turbine. Thus, it becomes necessary to maintain steam as dry as possible and it is necessary to monitor steam quality on a regular basis. The most commonly used method in determining steam quality is Throttling calorimeter. Here existing throttling calorimeter is designed for determining steam quality within a pressure range of 20 – 25 bar. This existing calorimeter is optimized for monitoring steam quality within a range of 4 – 12 bar gauge pressure. Pipe and orifice dimension of the calorimeter is calculated for a given flow rate of steam by using ISO norms and Bernoulli’s principle. After conducting multiple trials on newly designed model test rig it is found that the 4 mm orifice diameter model gives the greater consistency of results and it is considered to be an optimized model.


Introduction
Steam is the gas formed when water changes its state from the liquid to the gaseous. In steam-using industries, steam is commonly referred to as "Dry or Wet steam." Steam plays a vital role in the industrial revolution and is the major source for power generation in steam engines or steam turbine. In case of a thermal power plant, if available steam is wet then it results in corrosion and erosion of turbine blades. Thus, it becomes necessary to maintain steam quality high enough and it should be monitored on a regular basis. Hence, steam quality plays a vital role in determining the final product quality and its outcome.
The method used in monitoring steam quality is Tank calorimeter, Separating calorimeter, Throttling calorimeter, Separating-Throttling calorimeter and Electric calorimeter. Based on the availability of inline steam quality, above calorimeters are used for determining dryness fraction of steam.
If available steam is almost dry, we make use of a throttling calorimeter. Here a sample of steam is extracted from the main steam line and passed into the calorimeter through an orifice of known size. Steam throttles at the orifice and finally expands in the expansion chamber of a calorimeter. The overall expansion process of steam takes place adiabatically.
Modified throttling calorimeter is nothing but the modification of existing calorimeter which was designed for monitoring steam quality at 25 bar pressure. Here, existing calorimeter is modified by optimizing overall design of existing calorimeter to some lower size so that it can able to monitor steam quality up to 12 bar pressure. Also, existing model is modified without using a baffle.

Literature Review
Long et al. [1] described the method for determining the steam quality used in steam flooding for the secondary recovery of petroleum. Here, the convention throttling calorimeter is modified based on available thermodynamic properties of the steam. The process of automatic continuous operation along with heat addition was also described.
Chien [2] described the method of utilizing the pressure at the entry of a nozzle and the flow rate through a nozzle in calculating the quality of steam. The condition required is critical flow through a nozzle and discharge from a nozzle is to be condensed. Amount of condensed steam is measured and using this value steam quality is determined by utilizing standard formula.
Cheung et al. [3] described in detail about the method and apparatus for determining the mass flow rate and the quality of inline steam. In this case, the total flow of steam is directed towards the liquid-vapour separator where some amount of moisture is separated and measured. The flow of one of the stream is regulated to hold the level of the separated liquid constant. Thus, by obtaining the pressure and temperature of the separated flow upstream, the mass flow rate and the steam quality is determined.
Hayes [4] described in detail about how to calculate inline steam quality by using separating calorimeter. He stated that the separating calorimeter helps in removing the moisture content present in the steam that further helps in improving steam quality before it throttles. Here for moisture separation cyclone separator is utilized. Salunke [5] described the modified throttling calorimeter which helped in improving the performance and obtaining the correct quality of steam. In this case, the overall length of existing throttling calorimeter was reduced and modified by introducing a baffle which helps throttled steam to flow in U-path. The detailed information related to the general principle for methods of measurement and computation of the flow rate of fluid flowing in a conduit by employing pressure differential devices when they are inserted into a circular crosssection conduit running full was obtained through ISO 5167-1 [6].

Existing throttling calorimeter details
Existing throttling calorimeter shown in fig 1. features baffle plate. Since the throttled steam flow in U-path, the total length of steam travel is increased for the steady flow purpose (velocity profile will get stabilized.) On one side of the baffle, there is a jet of steam with high velocity after an orifice. After traveling some distance it flows to the other side of the baffle with lesser velocity where we can measure steady temperature, pressure.

Design of Orifice:
Throttling Calorimeter consists of orifice plate whose purpose is to throttle inline steam. Hence a proper dimension of an orifice is calculated by applying Bernoulli's principle at the inlet section and orifice  (1) and solving, value of D 2 = 4.05 mm. Thus, orifice diameter for a given mass flow rate and pressure is 4mm and Diameter ratio (β) is 0.2563.

Calculation of pipe diameter:
For a given orifice diameter, pipe diameter is calculated by using ISO norms. As per ISO 5167 -2 formula for determining pipe diameter is [5]:

CAD model of modified throttling calorimeter
Referring to the above calculation, the dimensions of orifice and pipe are i. Orifice diameter = 4 mm.

Inlet section Expansion section
The nearest standard pipe dimension of 15.8 mm i.e. 0.5 inch pipe size (15NB) is selected for modified calorimeter pipe. The CAD model as per above calculated dimension is shown in fig. 2 and fig. 3

Operating procedure and layout of modified throttling calorimeter
Step 1: Steam is extracted from the main steam line and is passed to inlet section pipe.
Step 2: Steam is then passed through PRV (Pressure Reducing Valve) and ball valve (BV).
Step 3: After opening the ball valve completely, steam passes through orifice plate where it throttles to atmospheric pressure. Steady state will be observed within 5 to 10 minutes of experiment startup.
Step 4: Note down the pressure and temperature before and after throttling through pressure gauge (PG) and temperature transmitter (TT). By using the steam table, properties of steam are calculated and steam quality is determined.
Working layout shown in fig. 4

Calculation of dryness fraction value
The amount of dryness of steam is determined by equating the enthalpy values i.e. enthalpy of extracted steam at known line pressure and enthalpy of expanded steam in the calorimeter. After noting down the pressure before and after throttling and temperature after throttling we can able to calculate the quality of steam by using isenthalpic principle as shown below

Dryness fraction of steam calculated with respect to available inline pressure
Results listed in table 1 show the dryness fraction of steam obtained at different available inline steam pressure.
Here, different inline pressures are obtained by regulating through pressure relief valve. Thus, through results, it is found that the value of dryness fraction is found to be within the accuracy of 0.5%.

Dryness fraction of steam calculated with respect to boiler pressure
Results listed in table 2 show the dryness fraction of steam obtained with respect to available boiler pressure. Thus, through results, it is found that the value of dryness fraction is found to be within the accuracy of 0.3%.