Analysis and Optimization of a Steam Generator System Based on the Rankine Cycle, Monografías, Ensayos de Ingeniería de Producción

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Abstract : this article will analyze the implementation of the most optimal proposal. To stabilize the behavior of the turbine, the stabilization process will be evaluated with three different proposals each with their relevant tests, to proceed to choose the most favorable for the process. The stabilization of the turbine behavior I a critical aspect since what we are looking for in this way is to maintain a stable output power. I. INTRODUCTION In this laboratory report we will show the behavior of the turbine we have in the pilot plant, we will show data and graphs of the input and output behavior; Three proposals for energy optimization will be shown. We will work only with the boiler and the turbine, without opening the way to the other elements. Our main objective is to stabilize the power released by the turbine. I. CONCEPTUAL FRAME The ideal Rankine cycle does not include any internal irreversibility and is composed of the following four processes: 1 - 2 Isentropic compression in a pump 2 - 3 Addition of heat at constant pressure in a boiler 3 - 4 Isentropic expansion in a turbine 4 - 1 Heat rejection at constant pressure in a condenser Fig 1. diagram of the steam generator system Fig 2. T-s diagram for the Rankine cycle. [1] The water enters the pump in state 1 as a saturated liquid and condenses isentropically up to the operating pressure of the boiler. The water temperature increases slightly during this isentropic compression process due to a slight decrease in the specific volume of water. [1]

ESTABILIZATION OF THE POWER GENERATED BY THE TURBINE

Duarte S. Ivan Andres, Duran H. Hermes, Medina M. Melitza, Toloza B Nino, Jaimes B. Robin. Faculty of Energy Engineering, UNAB Bucaramanga, Colombia

The water enters the boiler as a compressed liquid in state 2 and exits as superheated steam in state 3. The boiler is basically a great heat exchanger where heat originating in flue gases is transferred to water essentially to constant pressure. The boiler, together with the section (superheater) where the steam overheats, is called a steam generator. The superheated steam in state 3 enters the turbine where it expands isentropically and produces work by rotating the shaft connected to an electric generator. The pressure and temperature of the steam decreases during this process to values in state 4, where the steam enters the condenser. In this state the steam is usually a high- quality wet steam. The steam condenses at constant pressure in the condenser, which is basically a large heat exchanger, rejecting the heat to a low temperature, cooling medium such as a lake, a river or the atmosphere. The steam exits the condenser as a saturated liquid and enters the pump, completing the cycle. Such a power station uses the Rankine cycle. This is the cycle of the steam produced in the boiler, then taken to the Steam turbine (prime mover). From the turbine the steam is cooled back to water in the Condenser, the resulting water is fed back into the boiler to repeat the cycle. I. OPERATIONAL FRAME

Diagram design:

This diagram represents the instrumentation and control of the process constituted by the pilot plant steam generator system. It is based on a Rankine cycle and in this diagram, you can appreciate the different work teams that make up the Rankine cycle. A centrifugal pump that drives water and a stream of gas, feed the boiler to generate steam and thus pass through the respective steam turbine which in turn rotates the shaft to a DC generator. Subsequently, the steam passes through a condenser that, as this indicates, fulfills the action of condensing the steam coming from the turbine in order to finish the cycle in a condensate tank and in this way recirculate. Fig 2. P&ID diagram of the pilot plant steam generator system. Own source The PFD diagram of the steam generator system of the Pilot Plant, traces a representation of a process flow diagram where the process is developed. Based on a Rankine cycle, the steam generator system consists of their respective equipment: Centrifugal pump, boiler, steam turbine, condenser. Fig 3. PFD diagram of the pilot plant steam generator system. Own source. Centrifugal Pump The basic centrifugal pump consists of a rotating disk molded into vanes referred to as the impeller. The impeller is encased in a housing to channel and direct the produced liquid flow. Water enters near the center of the impeller; whereby motion is imparted to the fluid through the rotation of the vanes and the water is then discharged though the outlet of the casing. By varying the designs and arrangements of centrifugal pumps, they can be constructed to suit specific needs or requirements.[2] Boiler Fuel and air are mixed and burned in a furnace in this system. The result of combustion is the conversion of the chemical energy of the fuel into thermal or heat energy. The heat transfer surface in the form of tubes through which they circulate is aligned with the furnace. These tubes receive radiant heat from the flame and transfer it to the water side of the system.

TEST 1:

Analysis test 1: In this test what we performed was to reduce the delta pressure in the boiler, without bone regulation without using the second valve and with an opening distribution of 100%, where it is evident that the behavior remains unstable over the test time that was 40min, in the graph you can see the instability in the amplitude of the peaks. Table 2. average test 1 Graphic four. Power vs time test 1 TEST 2 Graphical analysis 2: In this test we kept the pressure delta to a minimum, but the distribution opening was reduced to 30% and without bone regulation without using the second valve, where it was evident that the behavior remained noticeable fluctuations over the test time that was 40min, in the graph you can see the instability in the amplitude of the peaks. Table 3. average test 2 Graphic five. Power vs time test 2 TEST 3: Graphical analysis 3: In this test, we kept the pressure delta minimum, we also maintained a distribution at 30% and with bone regulation using the second valve, where it is evident that the behaviors remained much more stable during the test that was 40 min, in the graph you can see the greater stability in the amplitude of the peaks. Table 4. average test 3 Graphic six. Power vs time test 2 Analisis General Graphical analysis 4: It can be seen that as we improve the turbine stability behaviour, fluctuations are reduced, but the generated power decreases. As can be seen in the graph, the most stable period was test three thanks to the reduction of the pressure delta, distribution to 30% and bone regulation using the second valve.

Graphic seven. Power vs time test complete process PROPOSALS

1. First proposal for regulation and consumption of generated power.

• INSTALLATION OF A STORAGE SYSTEM BY MEANS OF A BATTERY BANK. The proposal is based on the installation of a charge regulator connected to the DC direct current generator located in the PILOT PLANT engineering laboratory. The charge regulator feeds a storage bench consisting of a battery with a capacity of 100 [A/hour]. There is also a connection from the regulator to an inverter, which converts the DC input voltage to an AC output voltage. In this way the battery bank acts as a regulator of the power required by a system, as it constantly delivers the power independently of the power behaviour at the generator output. This proposal could provide electrical energy to a system regardless of whether it is alternating or direct current and is due to its configuration. Additionally, the batteries are charged independently of the operating conditions of the steam production cycle and the generation cycle. In this way the system would store energy regardless of the flows, pressures and temperatures supplied to the turbine or any other flow restriction or pressure regulation that occurs over the main steam distribution loop. Likewise, the charging cycles depend directly on the operation of the turbine and generator, in addition to the fact that the charge regulator has this cycle, which supplies the charge to the battery and indicates when they are fully charged. On the other hand, the discharge cycles are directly dependent on the consumption of a system to be supplied. This proposal derives from the systems installed in solar panel loading and storage systems and which can be observed on the roof of the engineering building L of the Autonomous University of Bucaramanga.

PROPOSAL ELEMENTS

• MPPT charge controller They are regulators usually used for charging battery banks in photovoltaic systems. These regulators are responsible for controlling the flow of energy between the generation field and the batteries. The MPPT regulators (Maximum power point tracking), have the ability to separate the operating voltage of the generation field from the battery voltage, therefore, not depending on the battery voltage, the MPPT algorithm can vary the operating voltage, checking at every moment which is the point of maximum power available. It basically consists of a protection diode, a DC-DC voltage converter and a maximum power point tracker. o The DC-DC voltage converter (from high voltage in the generation field to low voltage in the batteries) allows working at different voltages in the generation field and in the batteries.
• Batteries Batteries are devices that store electrical energy in chemical form and then release it as direct current in a controlled manner. All types of batteries contain one positive and one negative electrode immersed in an electrolyte, and the complete set is inside a container. Operation: The positive electrode is composed of lead dioxide and the negative of porous lead. When an electrical charge (e.g. headlights or a starter motor) is connected through the battery, a current flows through the battery electrolyte and through the external charge. This causes the battery to discharge, causing the chemical composition of both electrodes to be transformed into lead sulphate. To recharge the battery, a current must be passed through it from an external source of electricity such as an alternator, dynamo or charging unit. In this way, lead sulphate is transformed back into the original materials: lead dioxide and porous lead. As the battery charges, electricity begins to break down (hydrolyze) the water from the electrolyte into its constituent elements, hydrogen and oxygen, which are released in the form of gas. This is why batteries release gases when they are charged.
• Inverter An inverter is a static energy converter, which convert DC direct current into AC alternating current, allowing a load to be fed into its alternating output, regulating voltage and frequency. In other words, an inverter

energy is the proposed installation of an electrolyzer of cells for the production of hydrogen. SPECIFICATIONS OF THE ELECTROLYZER

• Price 600.
• 80.21% Efficiency
• Current 10 [A]
• Number of cells 7
• Input Voltage 12.9-14.1 [V]
• Temperature 20 to 50 [°C]
• Thickness 160 [mm] approx.
• effective plate area 85 [〖cm〗^2] SYSTEM CONNECTION BLOCK DIAGRAM The currently installed load (flooded resistance) is eliminated and the direct connection to the voltage regulator is made, from which the connections to the battery, DC/AC inverter and in the same way the load represented as the electrolyser are derived. There is a system that is quite simple in the installation of its components. IT SHOULD BE NOTED THAT THE IMPLEMENTATION OF THIS SYSTEM HAS MANY MORE FIELDS OF APPLICATION BECAUSE IT HAS GREATER AVAILABILITY BY THE USE OF BATTERIES AND THE INVERTER

2. Second proposal for the regulation and

consumption of generated power.

• REGULATION OF BOILER OPERATION AND

STEAM DISTRIBUTION.

This proposal is composed of two possible

configurations identified by the range in power

generated by the turbine operating at conditions of

regulation and restriction of steam flow.

A. FIRST REGULATION PROPOSAL WITH

IMPLEMENTATION OF EXISTING

PHYSICAL PLANT

The operating conditions of the steam production

cycle are restricted in the pressure delta with which

the boiler operates, decreasing a pre-established

delta from 12 psi to 8 psi, with a maximum pressure

of 125 psi. In addition, the steam flow is passed

through an independent loop connected to the main

loop before the steam distributor. In this

independent loop is located a pressure regulating

valve, manually operated by screw regulation, in

which the pressure of the steam is reduced to values

with little oscillation. Subsequently the flow is

restricted with an opening of 30% in the solenoid

valve located in the main steam distribution loop,

this condition is established so that the pressure

regulating valve operates more optimally and better

regulates the steam circulating through it. It should

be noted that the pressure regulating valve in the

circuit operates at medium and low steam flows.

condition is established so that the pressure regulating valve operates more optimally and better regulates the steam circulating through it. It should be noted that the pressure regulating valve in the circuit operates at medium and low steam flows. These operating conditions shown above were implemented in the generation circuit (boiler, turbines, generator, etc.) showing satisfactory results regarding the oscillation of the generated power data, where a favorable stability criterion was achieved with respect to other cases of analysis. Likewise, due to circuit operation configurations, optimal steam supply conditions are not provided to the turbine, with low power values (34-37) [W], average generated power of 35.5[W], average current of 1.1 [A], and average voltage of 32.27 [V].

In addition to the proposed regulation of conditions it is necessary to install two manometers, located before and after the pressure regulating valve existing in the system in order to determine regulation values. GRAPH OF THE BEHAVIOUR OF THE POWER GENERATED FOR VARIATION TESTS. The region enclosed and coloured with pink corresponds to the test with conditions mentioned above.

• CONSUMPTION OF GENERATED ENERGY

PROPOSAL 2a.

Through the use of a voltage regulating circuit, voltage oscillations are controlled in order to be able to regulate the voltage to a fixed value, in turn this element regulates the output current to a fixed value. Boiler pressure control. Steam distributor Pressure regulating valve Controlled electrovalve, flow regulator.

higher percentages of openings in the electrovalve of the main distribution line. This to provide greater flow and pressure to the turbine, and this way to generate higher values of power at the output of the generator. For this purpose, a commercial pressure regulating valve was sought, adjusted to the operating conditions of the system, and also to maintain a flow regulation to supply more constant steam conditions to the turbine and to maintain a similar behavior in the power generated in proposal 2. The installation of this new regulating element would be located in the main steam line, in front of the independent loop where the pressure regulating valve of small flows is located. It would be necessary to adapt the tube in order to install flanges where this new element can be mounted PILOT VALVE DP 27 SPIRAX SARCO Description according to brand: The DP range of pressure reducing valves precisely controls the downstream pressure, regardless of upstream pressure or load variations. Recommended for medium process or branch applications, for precise process control or where an external interface or remote adjustment is required. This versatile and compact valve provides many efficient and economical pressure reduction solutions. Suitable for working with steam, air or industrial gases, the DP series offers a wide range of control options. The DP27 is an updated version of the DP17 version, a leader in sales of Spirax Sarco piloted steam pressure reducing valves. It combines the high precision control of its predecessor with the ability to work in harsh environments, with easy maintenance and easier selection. EXPECTED GENERATION RESULTS With the implementation of the regulating valve and maximum openings of 60% in the steam flow solenoid valve, behaviors similar to those shown in case 2 are expected. For reasons of study and data compiled in tests with operation at different percentages of solenoid valve opening, without the influence of any other regulating device, an average figure of power generated with an opening at 50% flow will be estimated and it is taken into consideration that the influence of the pressure regulating valve stabilizes the power generation line over time, regulating the pressure at the minimum value presented in tests, taking into consideration a 10 psi pressure drop from the valve location to the turbine inlet (this figure is averaged according to data collection).

• Pressure regulated by valve: [80 psi].
• Turbine inlet pressure: [70 psi]
• Average turbine inlet temperature: [174.71 °C].
• Steam flow: 258.55 [lb/hour]
• Average power generated: 278.81 [W] CONCLUSIONS: According to the data analyzed in the pilot plant test and thanks to the knowledge Installation location of the new pressure regulating valve Diagram image. regulator. The DP27 has only one control spring for 0.2 to 17 bar. Diagram image. regulator.

provided by some teachers, we conclude that the best proposal for the stabilization of the power generated by the turbine and the use of the energy generated by it, is the following: A charge regulator will be implemented at the exit of the turbine, since although much more stabilization has been achieved, there are still small oscillations that with the charge regulator (battery) it will be possible to maintain constants. Once our values are constant over time we adapt it to an inverter which is a device that changes or transforms a direct current input voltage to a symmetrical alternating current output voltage, with the magnitude and frequency desired by the user. Once our alternating current voltage is obtained, we will use it to charge a battery, which once charged, can be used for multiple applications.

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