For power plants that make use of high energy boiler feed pumps, there is a risk that the boiler feed pump may experience cavitation and overheating at low load and start-up conditions. These plants make use of a leak off or recirculation system that diverts some of the flow back to the feed water tank, ensuring that a minimum flow through the pump is maintained at low load and start-up operating conditions. The recirculation valve, also known as a leak off valve, experiences a very high pressure difference and cavitation pitting is common due to the water being close to saturation. There are various ways in which the recirculation flow is controlled in the industry such as open orifice, on/off binary type control valves, automatic recirculation valves (ARC) or modern modulating leak off systems. The valves themselves can also be simple plug type or make use of pressure staging to reduce the risk of cavitation. This project involves modelling the flow system around the boiler feed pump and its control for the various architectures employed in Eskom. This is to assist in understanding the reasons for cavitation damage that is found in some recirculation valves as well as the low load capability of the system. Single stage components with extremely high pressure drops are singled out as components with the highest risk of cavitation in the systems. Although extremely high pressure drops are found across the leak off valves themselves, the majority of the valves are multistage valves which are specifically designed to accommodate cavitation development and are therefore not of major concern. Some of the findings of the study are: The rule of thumb used within Eskom to determine the amount of pressure reducing stages on leak off valves could be more conservative. The specification of new valves and components for the leak off systems requires accurate specification based on detailed process models, such as the ones developed for this study. The full range of all possible operational cases must also be considered during the design.

Boiler feed pump turbines (BFPTs) are in use at a number of Eskom power stations. They utilise bled steam extracted from the main turbine in order to drive multistage centrifugal pumps which supply the boilers with feedwater. With an increase of renewables in the energy mix, the need for Eskom’s coal-fired power stations to run for extended periods at very low loads has arguably never been this great. Various systems affect the ability of these generation units to run economically at low loads. One such system is the boiler feed pump turbine and its associated pumps. A station was selected from Eskom’s fleet based on access to information and the station being a relatively typical plant. The Unit (a boiler and turbogenerator set) selected for study was one with the most thorough instrumentation available for remote monitoring. The BFPT system of this Unit was modelled in Flownex, a one-dimensional thermofluid process modelling package. The model included individual pump stages, steam admission valves and a stage-by-stage turbine model utilising custom stage components. These turbine stage components represent each stage with nozzles and other standard Flownex components. The boundary conditions of the system were set as functions of generator load in order to represent typical values for use in case studies. The relationships between load and boundary conditions were based on large samples of data from the station’s data capture system (DCS). A corresponding standby electric feed pump system was also modelled in Flownex for a comparative case study. After model validation, a number of case studies were performed, demonstrating the functionality of the model and also providing specific results of value to the station in question. These results include the minimum generator load possible with different steam supplies; maximum condenser back pressure before plant availability is affected; the viability of changing the pump leak-off philosophy; and the effect of electric feed pump use on power consumption. The main recommendations from the case studies were as follows: i. to stroke the steam admission valves as per the design charts, ii. to test the operation of the BFPT down to 40 % generator load, iii. to keep the pump leak-off philosophy unchanged, iv. to maintain the cooling water system and condensers sufficiently to avoid poor condenser vacuum, v. to reconsider the decommissioning of the “cold reheat” steam supply, vi. and, to favour use of the BFPT over the electric feed pumps at all generator loads.

Fuel Optimization Unit (FOU) is part of an new system for the low pressure fuel circuit (LPFC) designed for Scania’s combustion engines. The system replaces engine mounted, mechanically driven, fuel feed pump and pre filter. One FOU variant (Type 1) pushes fuel through the pre filter using an additional electrical fuel pump and utilizes a small volume of fuel as a buffer, mainly to increase water separation performance. The second variant (Type 3) is similar to a conventional LPFC but uses an electric feed pump. The thesis investigate prerequisites and possible limitations when introducing FOU in Scania’s bus program. The investigation also compare Type 1 with Type 3 to determine if any technology is preferable. Among others, the investigation finds: • Type 1 is because of its size more difficult to house but is because of design less sensitive for placement in the chassis compared to Type 3. • CAN communication with electric fuel pumps risks disturbances due to potentially long cables. • Pressure drop in fuel lines is not identifies as an limitation for Type 1 but length is recommended to minimize on the low pressure side of the feed pump for Type 3. • There is an risk that fuel return temperature decrease between engine and fuel tank causing clogging of pre filter due to wax formation at low temperatures. • Number of start/stops and operating hours is a potential limitation for electrical fuel pumps. • Drainage of engine mounted main filter to the catch tank in FOU Type 1 may work non satisfactory if the fuel lines are routed badly. • The air conducted sound level caused by electrical fuel pumps is not identified as a problem. However, structural conducted sound may cause disturbance for passengers if the attachment is carelessly designed. Comparison between the variants indicates that Type 1 is preferable. Type 1 catch points mainly due to the use of catch tank but loses points mainly related to size, mass and complexity which results in a presumably high cost. Type 3 is similar to present LPFC but holds a number of advantages shared with Type 1. Both Type 1 and Type 3 are identified as clear improvements compared with current LPFC. / Fuel Optimization Unit (FOU) är en del av ett nytt lågtrycksbränslesystem avsett för Scanias förbränningsmotorer. Systemet ersätter motormonterad, mekaniskt driven, matarpump och förfilter. FOU utvecklas i två varianter som har gemensamt en chassimonterad elektrisk matarpump och förfilter. Den ena varianten (Typ 1) trycker bränsle genom förfiltret med hjälp av en ytterligare elektrisk bränslepump och utnyttjar en mindre volym bränsle som buffert bl.a. för att förbättra vattenseparering. Den andra varianten (Typ 3) liknar till stor del ett konventionellt lågtrycksbränslesystem men med elektriskt driven matarpump. Examensarbetet utreder förutsättningar och möjliga hinder att introducera FOU på Scanias bussar. I utredningen jämförs även Typ 1 med Typ 3 för att avgöra om någon teknik är att föredra. Utredningen finner bl.a. att:• Typ 1 är pga. sin storlek svårare att bereda plats för men pga. sin konstruktion mindre känslig för placering jämfört Typ 3. • CAN-kommunikation med elektriska pumpar riskerar störningar pga. potentiellt långa ledningslängder. • Tryckfall i bränsleledningar utgör ingen hinder hos Typ 1 men ledningslängderna bör minimeras på matarpumpens sugsida hos Typ 3. • Det föreligger en risk att returbränsletemperaturen svalnar såpass mycket mellan motor och FOU att förfiltret sätts igen av paraffinering vid kall väderlek. • Antal start/stopp och drifttimmar utgör möjligen en begränsning för elektriska pumpar. • Dränering av finfiltret på motorn till catch-tanken i FOU Typ 1 riskerar att fungera otillfredsställande om bränsleledningarna dras ogynnsamt. • Den luftburna ljudnivån från de elektriska bränslepumparna bedöms inte vara oroväckande hög men är beroende på infästning då strukturburet ljud kan vara störande för passagerare. Jämförelse mellan varianterna indikerar att Typ 1 är att föredra. Typ 1 får många pluspoäng i huvudsak förknippade med förekomsten av bufferttank men också med en hel del minuspoäng i huvudsak relaterade till storlek, vikt och komplexitet vilket också resulterar i ett förmodat högt pris. Typ 3 liknar till stor del befintligt lågtrycksbränslesystem men innehar en del tydliga fördelar som den till stor del delar med Typ 1. Både FOU Typ 1 och Typ 3 identifieras som tydliga förbättringar gentemot befintligt lågtrycksbränslesystem.

This diploma thesis focuses on designing impulse stage steam turbine to be used as the feed pump drive. I consecutively carried out thermodynamic calculation, seals and bearings layouts, with the aim to determine the steam mass flow through the turbine. Furthermore, I conducted turbine blade toughness check-ups, determined the rotor critical rotational speed, check-up rotor critical place (bearing pin) for torsion, and created a clutch screws design. The final part of this thesis pursues the other operating states of the turbine. This thesis is amended by a mechanical drawing of the turbine transection.

In this thesis I review the sufficient flow capacity of the safety valve against high-pressure heater thermal pressurization in high-pressure feedwater heater on nuclear power Dukovany. I present basic possible cases of thermal pressurization both a high node heater, and the extended pressure unit in case of closure all power heads to steam generators.