Hot Oil Boiler or Thermal Oil Boiler is used as a device to transfer heat from the heat receiving fluid (special thermal oil) and the heat giving fluid (hot gases resulting from burner combustion) by creating the necessary heat transfer surface, the heat of the gases from the burner combustion is transferred to the circulating thermal oil and causes its temperature to increase. In this device, high temperatures can be achieved at low pressures.
Water and steam are known as carriers of thermal energy in systems, and since working with steam and water at high temperatures requires higher working pressures, which is not cost-effective and lacks a high safety factor in a boiler or a hot oil boiler. A special oil is used as a substitute for water and steam and for this reason, it will be possible to reach 300 degrees Celsius at atmospheric pressure (to reach a temperature of 300 degrees Celsius with water and steam fluid requires a working pressure equal to 85 bar).
In addition to lower working pressures, using hot oil instead of water and steam at high temperatures has many other advantages, including the following:
- Small volume
- Saving fuel
- Ability to install and set up in a simple space
- Easy management and operation
- Unlimited heat capacity
- No risk of corrosion and damage caused by freezing
- Much less noise compared to steam boilers
- No heat loss through condensation
- No need for preliminary operation of feed water
- Less time to reach the desired temperature compared to steam boilers
Mechanical equipment for hot oil boilers
The main and practical body of a hot oil boiler consists of various parts, including:
1-Shell and Body
2- Heating Coil
3- Door and Skid
Also, the hot oil boiler must have the following equipment and accessories for proper operation:
- The burner (boiler) is gas-burning, diesel-burning, and diesel, or double and triple, depending on the type of fuel used.
- Electrical panel and control circuit and pressure switches
- Relief valve
- Circulator pump with calculated head and flow, which is floodproof.
- Line filling pump
- Main valve / Water valve / Drain valve / Air valve
- Expansion source to control oil volume expansion
- Oil storage source
- Control equipment and safety alarms
Types of hot oil boilers:
Hot oil boilers are divided into two types, horizontal and vertical, according to their capacity and design specifications, as well as the type of placement, each of which has its own advantages and disadvantages. Vertical boilers are usually used in low capacities or due to space limitations. Also, horizontal boilers usually have higher efficiency.
Advantages of vertical oil boilers
- Requires less space for installation
- Faster draining of oil from the boiler
- Better retention of heat in the boiler
Advantages of horizontal oil boiler
Absence of failure and burning of the burner
Easy opening and closing of doors
Easy and convenient adjustment of the torch
Easier service than vertical boilers
Easier to use and operate
Scope of application of hot oil boiler
The use of hot oil boilers and its use is preferred to hot oil boilers due to its many advantages and wide range of applications in various industries. Because the hot oil boiler produces more heat than the hot oil boiler and the temperature control in the boiler is done in an easier and more convenient way. For this reason, hot oil boilers are used for applications that require high temperature and indirect control, which include chemical industries (production of petroleum products, dyes and solvents, polymerization machines and production motor and industrial oils, as well as grease production, etc.) textile industries – food industries – bitumen production industry, etc.
Advantages of hot oil boiler
- Less time to reach the desired temperature compared to steam boilers
- Working at high temperature and low pressure and more safety and reliability
- No need to perform purification and pre-purification operations
- No need to perform purification and pre-purification operations
- Ease of use and reduced maintenance options
- No heat loss – no formation of deposits and corrosion
- High reliability factor in body design and internal components
- Easy installation
- Small volume with the ability to install and operate in small spaces
- Good quality and high material used in it
- Less noise compared to steam boilers
Key points in using heat transfer oils
Selection of appropriate thermal oil:
Depending on the type of system and the required operating temperature, the appropriate thermal oil should be used. Oxidation and the formation of coke and sludge is one of the cases where the use of inappropriate mineral oils, especially at temperatures above 300 degrees Celsius, occurs in the hot oil boiler system, especially for temperatures above 300 degrees, silicone oils should be used.
Thermal oil analysis in specific time periods:
Sampling and checking the quality of the thermal oils that are used in the system in certain periods of time gives sufficient information about the current pollution and the desired quality of the oil which will play an effective role in preventing problems and damaging the hot oil system.
Prevent water ingress:
The occurrence of cavitation phenomenon in the pump and making noise in the hot oil system is one of the effects and results of water entering the system, which on the other hand will cause the desired temperature not to be reached and due to the increase in temperature and turning into steam, it will experience a huge volume increase in the system.
Overhaul of the system
The possibility of fire due to the flash and low viscosity of fuel solvents and on the other hand causing leakage in sensitive sealing points such as flanges, etc. It is better to use special oils (flushing oils) for this purpose.
Material that can be used in hot oil boiler design
An important and very significant item in the design of a hot oil boiler is to include safety issues and the use of suitable materials. Due to the high temperature of the oil, any negligence can lead to financial and life damages and serious fires. In the construction of hot oil boilers, high-quality and standard tools and raw materials must be used based on clearly defined rules.
The hot oil boiler is usually produced as a single coil, two coils or three coils based on the capacity. All sheets used in the shell, combustion chamber and drum in the construction of hot oil boilers must be of DIN17155-17MN4 type. These types of sheets are special for making hot oil boilers and have high tensile strength. Also, the consumer pipes must be fire-resistant according to DIN17175-ST35.8 standard. The use of sheets and pipes outside the defined standard and with a thickness less than the permissible limit will reduce the life of the boiler and bring many risks.
The hot oil boiler must be equipped with a control system with quality and reliable equipment, so that in case of any problem, such as increasing the oil temperature beyond the permissible limit, no oil circulation, etc., it will automatically prevent the boiler from continuing by cutting off the burner.
Calculations and estimates of hot oil boiler capacity
The estimation of the highest and lowest thermal levels will be available to engineers and designers, based on which they consider the temperature changes and stresses that occur in the pipes due to the heat that enters them and based on that they prepare a plan. Obtaining the final map and its computational confirmation will be the start of the work of the executive team, which will start the construction of the device based on the internationally defined criteria and standards.
