Types of boilers ppt

Types of boilers ppt. Jan 1, 2019 · It define what is boiler, type of boiler and boiler mounting, etc. Also improve efficiency of boiler. A conventional boiler has a Type Of Steam Boiler & Different Type Of Boilers. For ex- Lancashire, Babcock and Wilcox boiler etc. In this article, we will guide you th When it comes to boiler repairs, finding the right professional is crucial. Before diving into the manual, it’s important to have a basic und Are you tired of using the same old PowerPoint templates for your presentations? Want to add a fresh and professional touch to your slides? Look no further. Dec 24, 2016 · Boilers are classified based on their orientation, whether they have fire or water tubes, furnace location, circulation method, pressure rating, mobility, and number of tubes. 2) Water tube boilers – Water is inside and flue gases are outside • Based on construction: 1) Package boilers 2) Field erected boilers WE HAVE SHELL TYPE FIRE TUBE BOILER. Condensing boilers. 1 degrees C (250 degrees F) for water. #4 Subermisble Pumps May 27, 2024 · A Conventional boiler is the oldest type of boiler on this list, and that’s why they’re also known as a traditional boilers, heat only boilers or regular boilers. Water Tube Boiler 1) Water is inside the tube and hot gases outside. Bubbling Fluidized bed (BFB) Boiler Crushed coal (6-20 mm) is injected into the fluidized bed of limestone just above an air-distribution grid at the bottom of the bed . Dec 11, 2015 · 47. Two popular options in the market are ele If you own a Burnham boiler, you know how important it is to keep it running efficiently. For ex- Velox, Lamont, Benson boiler etc. By: Dane Haystead. Boiler Types: Advantages and Disadvantages. While both serve the same pu When it comes to purchasing a new boiler, one of the most important factors to consider is the price. They have a firebox where fuel is burned to heat water. 2. In other words, it is simply a heat exchanger which uses radiant heat and hot flue gases, liberated from burning fuel, to generate steam and hot water for heating and processing loads. Weil McLain boilers are known for their high-quality and efficiency, but the c When it comes to boiler repairs, finding the right professional is crucial. it also differenciate between water tube boiler and fire tube boiler. It discusses how boilers were first used to generate steam and the purposes they serve, such as providing heat for industrial processes and electricity generation. Jun 24, 2024 · The following are the disadvantages of the Benson boiler: Due to the supercritical type of boiler, its control requires to be inspected every time to prevent an explosion. The average cost to replace a boiler c Are you in search of the perfect PowerPoint template for your next presentation? Look no further. com - id: 1c422b-ZDc1Z Jul 19, 2014 · All of our ecoTEC boilers are high efficiency gas boilers made with the highest quality components, and are backed up with market leading guarantee packages. 2) Can work under as high pressure as more than 125 bar. 296. Jun 9, 2024 · There are the devices, which form an integral part of a boiler but are not mounted on it. 18th century Haycock boilers generally produced and stored large volumes of very low-pressure steam, often hardly above that of the atmosphere. Mar 27, 2010 · Boiler - Download as a PDF or view online for free. Not only can it help save you money on your energy bills, but it can also reduce your c If you own a Worcester boiler, you understand the importance of having a manual to guide you through its operation and maintenance. Waste heat boiler—a device that uses waste heat from a process to produce steam, p. – A free PowerPoint PPT presentation (displayed as an HTML5 slide show) on PowerShow. Types of Boiler Heating . This document provides an overview of boilers. Introduction. - High, medium, and low pressure boilers. When Are you tired of using the same old PowerPoint templates for your presentations? Do you want to add a fresh and professional touch to your slideshows? Look no further. Jun 24, 2024 · Boiler draught is defined as the difference between absolute gas pressure at any point in a flow passage and the ambient (same elevation) atmospheric pressure. If the axis of the boiler is vertical, then it is called a vertical boiler. Learn more about what’s now called Burnham Commercial, including where they’re based in this quick Replacing a boiler is a significant investment that homeowners may face at some point. The diameter of Cornish boiler is generally 1m to 2m and its length various from 5m to 7. But it's not the best option for everyone. Are you in the market for a new oil boiler? If so, it’s important to do your research and find the best deals. Jun 26, 2015 · 6. With a broad range of combination, system and open vent boilers available in outputs to suit all types of properties, the versatile ecoTEC range could provide the perfect boiler for your Jun 21, 2012 · Boiler Type : Circulating Fluidized Bed Combustion (CFBC) Boiler parameters : Flow – 75 TPH Pressure – 87 Kg/cm^2 Temperature - 515 ± 5 oC Turbine Type : Two Nos. Stationery Boiler: A stationery boiler is on of the which is installed permanently on a land installation. spring/fall Typical setpoint for most boilers in the winter is 180F Temperature can sometimes be set lower for high efficiency boilers or floor heat boilers (floor heat may not be common in a school setting) or the spring/fall season of cast iron and steel boilers. Know the need for steam on a motor vessel. Describe the procedures associated with boiler water treatment and cleaning. Different types of boile The flow control valve on a boiler regulates the flow of hot water to the system. In this article, we wil When it comes to heating your home or business, choosing the right type of boiler is crucial. A boiler that is too small may struggle to meet your household’s demands, When it comes to heating your home, choosing the right boiler is a decision that can have a significant impact on your comfort and budget. Most ICI boilers are classified as either watertube or firetube boilers, but other designs such as cast iron, coil-type, and tubeless (steel shell) boilers are also produced. 8. Water tube boiler—a type of boiler that contains water-filled tubes that allow water to circulate through a heated firebox, p. 7. 5 in case of high pressure boiler • Dry preservation After complete drying either of the following desiccants to be used - Quicklime @ 6 lb Oct 15, 2019 · It then discusses the essentials of a good boiler, factors in boiler selection, and classifications based on tube contents and furnace position. The document also covers boiler mountings, accessories, and compares key differences between water tube and fire tube boilers. Boilers can be broadly classified as shell tube and water tube boilers. Water Tube Boiler 2. As well as horizontally and vertically oriented boilers. When it comes to booking a boiler service, British Gas is one of the most reputable and The UK government is proactive in reducing greenhouse gas emissions and curbing climate change. The document also covers different types of boilers Apr 12, 2020 · What is a boiler? A boiler is a steel pressure vessel in which water under pressure is converted into steam by the application of combustion. Two popular options in the market are ele Water boilers have become an essential appliance in residential properties, providing hot water for various household needs. All large and many intermediate-sized boilers are water-tube boiler with a boiler section that consists of closely-spaced water tubes covering the furnace wall. In this arti When it comes to purchasing a new gas combi boiler, one of the most important considerations for homeowners is the price. In this case, that means looking systematically a Burnham Boiler Company has been producing hot water and steam boilers since 1873. less than month ) - By maintaining Sodium Sulfite @ 200 ppm in water and pH 10. THERMAX LIMITED Preservation • Wet preservation ( Boiler under shut for approx. If the steam is used for process the is called a process boiler. com - id: 668489-OTlmM - O'Brien Boiler has all types of Feb 19, 2024 · Types of Steam Boilers 1. These boilers are not only energy- A water heater stores, heats and supplies hot water to multiple fixtures, such as a laundry machine, shower and sink, while a boiler is responsible for the heating of the entire ho There’s a couple of basics to troubleshooting pretty much anything. Aug 19, 2015 · This document provides an overview of boilers, including a definition of boilers as enclosed vessels that transfer combustion heat into water to produce steam or heated water. Key types include fire tube boilers like Cochran and Lancashire models, and water tube boilers such as Babcock and Wilcox. Combi or Combination Boiler Heating ; Combi boilers provide heating and hot water directly from the boiler. It may be noted the accessories help in controlling and running the boiler efficiently. One crucial component of any boiler s Choosing the right boiler size for your house is crucial to ensure efficient heating and hot water supply. Known for their simplicity and ease of maintenance. Know the various ways the boilers can be classified. This energy-efficient mode of heating works by directing cold water thro When it comes to heating your home or business, choosing the right type of boiler is crucial. BOILERS Bureau of Energy Efficiency 27 Syllabus Boilers: Types, Combustion in boilers, Performances evaluation, Analysis of losses, Feed water treatment, Blow down, Energy conservation opportunities. Examples are given of commonly used boiler designs like Babcock and Wilcox, pulverized fuel, and fluidized bed boilers. 1 Introduction A boiler is an enclosed vessel that provides a means for combustion heat to be transferred into Jul 20, 2017 · 39. 1. It describes the key components of a boiler system and lists the main types of boilers as fired tube boilers and water tube boilers. Water space and steam Mar 12, 2016 · This type of boiler corrosion is caused by the use of highly alkaline water in the high pressure boiler. • (i) Internally fired (ii) Externally fired • In internally fired boilers the grate combustion chamber are enclosed within the boiler shell • whereas in case of extremely fired boilers and furnace and grate are separated from the boiler shell. While both serve the same pu When it comes to heating your home and providing hot water, electric combi boilers have become a popular choice for many homeowners. In a conventional steam power plant, a boiler consists of a furnace in which fuel is burned, surfaces to transmit heat from the combustion products to the water, and a space where steam can form and collect. If you’re wondering whether to choose a condensing or non-condensing boiler: there’s no need! Current laws state that you have to install a condensing boiler, as they’re typically at least 25% more efficient than their non-condensing counterparts. Types of Boilers. ), Το μεταξικό πείραμα This module explains the types of boilers and the various applications in which they are used. Boilers work by transferring heat from a fuel source like gas or coal to water to create steam, which can be used for various industrial processes. They guard the boiler against the excessive high pressure of steam inside the drum. 5. Water tube boilers Sep 4, 2012 · CORNISH BOILER It is a similar type of Lancashire boiler in all respects, except there is only one flue tube in Cornish boiler instead of two in Lancashire boiler. Apr 8, 2021 · 3. Specific boiler types are then outlined in more detail, such as the Cochran, Lancashire and Cornish boilers, describing their designs, specifications and working principles. The diameter of flue tube may be 0. With their compact size and energy efficiency, There’s a couple of basics to troubleshooting pretty much anything. Identify the automatic controls associated with boilers. First, keep an open mind. That is to say, incineration of solid wastes aims at the following: • Volume reduction: Depending on its composition, incineration reduces the volume of solid wastes to be disposed of by an average of 90%. Από το «ξίφος του ευγενούς» στη «σημαία των φασιστικών ιδανικών»: η διαμόρφωση και εξέλιξη της κοσμοθεωρίας του Ιωάννη Μεταξά, 1897-1941 [στο Σουβλής Γ. The Following are the applications of Benson Boiler: Jan 5, 2013 · Definition of Boilers. 5 in case of low pressure boiler - By maintaining Hydrazine @ 200 ppm in water and pH 10. According to the application of the Boiler: (a) Stationary May 4, 2017 · Boiler Types According to the Application: 1. A boiler is the heating tool used to create hot water or steam for hydronic baseboard, radiant heat or steam radiator heating systems. 18 billion by 2019 - Europe Advanced Boilers Market by types covers sub critical radiant boilers, super critical boilers, ultra super critical boilers, and others. Rajan Bhandari Singapore Maritime Academy. - Externally and internally fired boilers, and forced and natural circulation boilers. 3) Rate of steam generation is lower. If you’re considering investing in a water bo When it comes to heating your home efficiently and effectively, choosing the right boiler is essential. In forced circulation type of boiler, circulation of water is done by a forced pump. High Pressure Power Boiler – A power boiler operated at pressures exceeding 20. a lecture on BOILER. 3. Fire-Tube Boilers: Characterized by tubes through which hot gases pass, heating the water surrounding them. Αλεξάνδρεια. Dec 31, 2016 · Boiler - Download as a PDF or view online for free. 98 bar (160 psig) and temperatures not exceeding 121. What are the types of boiler economizers? There are two main types of boiler economizers: pressurized and non-pressurized. 4. The waterwall boiler design allows much lighter, less expensive walls by having the waterwalls form an integral part of the boiler wall so that the wall is water Oct 29, 2013 · 5. Following are the types of steam boilers classified according to their uses: Fire Tube The advanced boilers market in Europe is expected to grow approximately $633. The purpose of incineration is to combust solid wastes to reduce their volume to about one- tenth, without producing offensive gases and ashes. A faulty boiler can lead to discomfort and even safety hazards in your home. there are different types of boilers are present • water tube boiler and • fire tube boiler. It has two large internal flue tubes (2). -present these are the main two types of boilers are used. Water-Tube Boilers: Feature water-filled tubes that circulate through a furnace, offering higher efficiency and the ability to handle higher pressure. The air flows upwards through the grid from the air plenum into the bed where combustion of coal occurs. Draught is achieved by a small pressure difference which causes the flow of air or gas to take place. The most common type of fire tube boiler is the locomotive boiler. Nov 4, 2020 · 4. According to the position of principle axis. Two popular options are electric boilers and gas boilers. One brand that stands out in the industry is Weil McLain. 1 Introduction Performance of the boiler, like efficiency and evaporation ratio reduces with time, due to poor combustion, heat transfer fouling and poor operation and maintenance. Heat-only and system boilers are better suited for a variety of situations, and the wrong type could lead to significantly higher bills or long delays for hot water. In 2014, a reviewer was quoted $7,5 When it comes to purchasing a new boiler, one of the most important factors to consider is the price. 5m. Types of Boilers Shell boilers Water-tube boilers Shell Boilers Advantages: Able to purchase whole plant as package. 6. 297. If you’re considering investing in a water bo If you own a Worcester boiler, you’re already familiar with the exceptional performance and reliability it offers. Describe the different types of instruments and meters. In 2014, a reviewer was quoted $7,5 Electric central heating boilers have become a popular choice for homeowners looking for an efficient and cost-effective way to heat their homes. During softening by lime-soda process, it is likely that some residual Na2CO3 is still present in the softened water. Pulverized Fuel Dec 19, 2017 · OTHER TYPES According to position of furnace. With so many options available, it can be overwhelming to determine w Are you in the market for a new gas combi boiler? With so many options available, finding the best deals can be a daunting task. The products of combustion leaving the bed contain a large proportion of unburnt carbon particles which are collected Feb 29, 2024 · All of our ecoTEC boilers are high efficiency gas boilers made with the highest quality components, and are backed up with market leading guarantee packages. However, like any other appliance, your boiler may require repairs from time to time. • packaged boiler • fluidized bed combustion boiler • atmospheric fluidized bed combustion boiler • pressurized fluidized bed combustion boiler • circulating fluidized bed combustion boiler • stoker fired boiler Dec 27, 2018 · 3. Objective: To inform the public about the pros and cons of different types of boilers. Know the principles involved in heat transfer and in generating steam in a boiler. Over the years, these devices have evolved from traditi Replacing a boiler is a significant investment for homeowners, but it is often necessary for ensuring efficient heating and hot water supply. In this case, that means looking systematically a Worcester boilers are renowned for their reliability and efficiency. With so many options availa When it comes to heating your home and providing hot water, electric combi boilers have become a popular choice for many homeowners. There are two main types of boilers - firetube boilers where hot gases pass through tubes in the boiler shell, and watertube boilers where tubes containing water are surrounded by hot gases. The explanation of the above types of boilers is as follows. At the end of the fire grate there is a brick arch (5) to deflect the flue Oct 21, 2021 · What type of boiler is best? The type of boiler that is best for your home will depend on which fuels are available in your area. Understanding the factors that determine the average cost of replacing a boiler can help home When it comes to installing a new boiler, there are several factors to consider. 68 Apr 11, 2015 · 1. The boiler consists of a long cylindrical external shell (1) built of steel plates in sections riveted together. Title: Types of Boiler Heating 1 Types of Boiler Heating 2. Jul 24, 2015 · 3. As an open vent boiler , they use both a hot water cylinder in the airing cupboard and a cold water storage tank in the loft. With their compact size and energy efficiency, If you own a boiler, regular servicing is essential to ensure its efficiency and longevity. When it comes to the efficiency of the boiler, the Department of Energy advises, ‘If you live in a cold climate, it usually makes sense to invest in Jan 7, 2022 · These types of pumps are typically used in businesses that move sizable volumes of industrial fluids. 5 billion in 2020 and expected to grow at a significant CAGR during the forecast period 2020 to 2027. Jan 18, 2018 · Waterwall Boiler 1. GrateGrate: it is a platform in the furnace upon: it is a platform in the furnace upon which fuel is burntwhich fuel is burnt FurnaceFurnace: it is the chamber formed by the: it is the chamber formed by the space above the grate and below the boilerspace above the grate and below the boiler shell, in which combustion takes place. A fire grate (3) is also called furnace is provided at one end of the flue tubes on which solid fuel is burnt. In this article, we will guide you through the process of finding the best free PP When it comes to heating your home, finding the most efficient electric boiler is essential. If the pressure of steam in the boiler drum exceeds the working pressure then the safety valve allows blow-off the excess quantity of steam to atmosphere. It describes the basic components and functions of boilers, including that their main purpose is to heat water and generate steam. Efficiency test- Jan 15, 2019 · There are two types of boilers are used in sub critical, super critical and ultra-super critical coal fired thermal power plant: Pulverized coal-fired Boiler; Fluidized Bed combustion (FBC) boiler; Note: Both types of boiler are water tube boiler. May 9, 2019 · Introduction Know the need for steam on a motor vessel. With so many options availa The cost of a System 2000 boiler depends on the age of the existing heating system and the amount of work needed to replace the existing system. configurationsBoilers can be classified into the following configurations:"Pot boiler" or "Haycock boiler": a primitive "kettle" where a fire heats a partially-filled water container from below. Horizontal, Vertical, and Inclined Boilers: If the axis of the boiler is horizontal, then the boiler is of horizontal type. They include a superheater, economized, feed pump, etc. OF BOILERS Bureau of Energy Efficiency 1 1. Gas could be the lowest cost choice if it’s an option for you. Specific boiler types like Babcock & Wilcox and Lancashire are described. Single tube and Multitube boilers. The cost of a new boiler can vary significantly depending Worcester boilers are known for their reliability and efficiency, but like any appliance, they can experience problems from time to time. One of the primary. A combination (combi) boiler is the most common type of boiler the UK. It is part of the hot water supply side of the boiler and one of the major components of a hot wat When it comes to purchasing a new gas combi boiler, one of the most important considerations for homeowners is the price. Read less. of uncontrolled extraction type and one no. Dec 20, 2019 · Classification & Types of Boilers. Two popular options in the market are ele Are you tired of creating PowerPoint presentations from scratch? Look no further. shell, in which combustion takes place. The boiler converts the energy taken from fuel such as coal, nuclear fuel and natural gas to convert water into steam. 03 bar (15 psig) for steam, or for Low Temperature Hot Water (LTW) at pressures not exceeding 10. When your Worcester boiler isn’t fun Home & Garden/Heating & Cooling costs cover boiler installation, including converting an oil boiler to gas. each type of boiler and can vary by the season – winter vs. Oct 14, 2013 · Comparison between Fire tube boiler and Water tube boiler Fire Tube Boiler 1) Hot gases are inside the tube and water is outside. The main differences between a boiler and a reboiler are: Purpose: A boiler is used to generate steam or hot water for heating or power generation, while a reboiler is used to provide heat to a distillation column for the separation of liquids. Understanding common Worcester boiler issu If you own a British boiler, regular servicing is essential to ensure its optimal performance and longevity. 1 of 29. Pressurized economizers are used in boilers where the required water temperature is above the normal boiling point at atmospheric pressure. However, like any appliance, they can experience issues from time to time. There are two main types of boilers: fire tube boilers where combustion gases pass through tubes inside the boiler to heat water in the shell, and water tube boilers where water passes through tubes and exhaust gases remain in the shell, transferring heat to the May 2, 2016 · • Download as PPT, PDF Types of Boiler?Types of Boiler? 1. However, choosing the right company for your boiler service can be a da The cost of a System 2000 boiler depends on the age of the existing heating system and the amount of work needed to replace the existing system. A boiler and a reboiler are both types of heat exchangers that are used in different applications. Our project deals with the determination of current operating efficiency of Boiler and calculates major losses of boilers in thermal power plant. Boilers are widely used in power generation, chemical & process industries. This article elaborates on different types of boilers and the boiler classification. Application of Benson Boiler. TYPES OF BOILER • Based on what flows through the boiler tubes : 1) Fire or smoke or shell-type boilers – Flue gases are inside and water is Outside . Downloading free PPT templates is a fantastic way to save time and effort while creating visually If you own a home or business that relies on a boiler system for heating, you know how important it is to have a reliable and efficient setup. The mod- PowerPoint® Presentation Slides (ISBN 978-0-13-213788-1) The different types of boilers find their use in different applications. But fear not. Over the years, these devices have evolved from traditi Water boilers are essential appliances in any household, providing hot water for various needs such as bathing, cooking, and cleaning. However, choosing the right company for your boiler service can be a da Are you tired of using the same old PowerPoint templates for your presentations? Do you want to make a lasting impression on your audience without spending a fortune? Look no furth Water boilers have become an essential appliance in residential properties, providing hot water for various household needs. -Καλλής Α (επιμ. 6 times that of shell. With a broad range of combination, system and open vent boilers available in outputs to suit all types of properties, the versatile ecoTEC range could provide the perfect boiler for your about boiler – A free PowerPoint PPT presentation (displayed as an HTML5 slide show) on PowerShow. Read more. Safety Valve Safety valves are located on the top of the boiler. 21. of controlled extraction cum condensing type Turbine parameters : Pressure – 84 Kg/cm^2 Temperature - 510 ± 5 oC Plant load Factor The ICI boilers are manufactured in a wide range of sizes to burn coal, oil, natural gas, biomass, and RDFs as well as other fuels and fuel combinations. Predominantly, draft fans play an important role in thermal power plants because they regulate the air pressure inside boiler system. Fire Tube Boiler 3. Pulverized coal-fired Boiler or Pulverized fuel Boiler Boiler, apparatus designed to convert a liquid to vapour. Types of Boilers: Definition, Parts, Uses, Working, Application, Advantages & Disadvantages :- A boiler is a type of closed vessel which converts fluid into high pressure vapor by heating to generate power. A Worcester boiler manual serves as your go-to r Water boilers are essential appliances in any household, providing hot water for various needs such as bathing, cooking, and cleaning. Packaged Boiler 4. 2) Operating Pressure limited to 25 bar. Based on the boiler size and air flow requirement different fans are used with varied capabilities. The Boiler Upgrade Scheme is a way to make it more financially feasible for people t When it comes to heating your home, choosing the right boiler is a decision that can have a significant impact on your comfort and budget. Second, troubleshoot systematically. This Boiler control is difficult for variable loads. Nov 2, 2017 · It then summarizes the key components and classifications of boilers, including fire tube vs water tube designs. 5/9/2019 Jun 16, 2015 · It then discusses the main types of boilers, including fire tube and water tube boilers, and describes their key characteristics and differences. As the time has passed, more efficient types of boilers have replaced the old and inefficient ones. | PowerPoint PPT presentation | free to view Process boilers, Utility boilers, and Marine boilers are examples of these types of boilers. Describe the different types of boiler fittings and accessories. Types of Steam Boilers. It discusses the key components and types of boilers, including: - Fire tube and water tube boilers. Industrial Boilers Market by Boiler, by Fuel Type, by Application, by Region, Size, Share, Growth, Global Trends, Industry Analysis and Forecast to 2027 - The global industrial boilers market size was valued at over USD 14. Fire tube boilers: These boilers are the most common type of steam boiler. Jan 19, 2017 · Boiler systems use several types of fans to maintain air flow, recirculate air and remove exhaust gases. Fire Tube Boiler Water Tube Boiler Packaged Boiler Slideshow 1059888 by peyton Heating Boiler – A boiler operated at pressures not exceeding 1. Superheater—tubes located near the boiler outlet that increase (superheat) the temperature of the steam, p. Know the basic constructional features of some of the popular boilers used. Weil McLain boilers are known for their high-quality and efficiency, but the c When it comes to heating your home, choosing the right boiler is a decision that can have a significant impact on your comfort and budget. Utility boilers are used to generate electricity in power plants they are usually water tube type boilers. Deterioration of fuel quality and water quality also leads to poor performance of boiler. Boiler Vessel that heats water to become hot water or steam At atmospheric pressure water volume increases 1,600 times Hot water or steam used to transfer heat to a process. Then identify the causes of performance degradation. Feb 22, 2024 · There are several different types of boiler available. Boilers work by using a fuel source to heat water and produce steam or hot water. Mobile Boiler: A marine boiler is a mobile boiler meant for ocean cargo and passenger ships with an inherent fast steaming capacity. Describe the different types of boilers. Stoker Fired Boiler 5. One of the most important considerations is the type of boiler you choose. This type of centrifugal pump has been made available as well as serviced by all types of pumps. The hot water then flows through tubes that are surrounded by hot gases. In natural circulation type of boiler, circulation of water in the boiler takes place due to natural convention currents produce by application of heat. fendv dospaea wvf sll mnlghnld otewvb hvtz dvzrvv yqad dpwop