Solar furnace

Solar furnace

Heat consumption for cooking is always present, regardless of climatic conditions and financial capabilities of the population (no one eats raw potatoes or cereals).

Heat consumption depends on many factors: demographic (number of members and family composition, diet and diet, taking into account national traditions); organizational (provision of catering enterprises, an increase in the use of semi-finished products in home meals); in the countryside, there are high costs for fodder preparation. And also technical: the introduction of new improved devices that ensure an even distribution of the heat flow and maintain an optimal mode in the cooking process, the introduction of dishes with special coatings. Also, the amount of electricity consumed largely depends on the culture of consumption and preparation of products: there are significant differences between countries and regions..

In North America, Europe, Australia, New Zealand, the main cooking devices are ovens, stoves and microwaves. Cooker hoods and small kitchen appliances – coffee makers, compact bread ovens and others – can also consume a lot of energy. Rice cookers are widely used in Japan and other Asian countries. Most of the energy in cooking is expended in heating it up. A small amount is used to defrost frozen food. As for the type of energy, little electricity is consumed for cooking, mainly natural gas or liquefied petroleum gas is used, including in the CIS countries.

In the early 80s. XX century in China, the efficiency (efficiency) of wood-burning stoves was about 10%. An Efficiency Improvement Program was adopted: first up to 20%, and then up to 30%. Thus, by the end of the 90s. more than 180 million of these stoves were installed in China in households (90% of the total number of rural households in China).

The cooking process and the inextricably linked hot water supply for domestic consumers requires significant amounts of energy (table 1).

Process Public sector Residential sector
Hot water supply 1030 126
Cooking food one hundred 150

Table 1 – Annual standards of heat energy demand for municipal consumers, thousand kcal / person • year

Heating foodstuffs provides, including the implementation of sanitary and hygienic measures – when heated above 80 ° C, the microorganisms contained in them are destroyed. This circumstance is very important, since in the overwhelming majority all food raw materials of both plant and animal origin are seeded with various microorganisms, among which there are many harmful and pathogenic.

And the second thing. It is widely known that the boiling regime after boiling is of great importance to improve the quality of culinary products. Violent boiling in most cases negatively affects the quality of food: broths become cloudy, products are deformed, losses of aromatic substances and vitamins increase, etc. Porridge, pasta, sauces should be cooked at a temperature of 85 – 90 ° C, fish, poultry, meat – at 85 – 95? C.

By changing the traditional method of cooking (if it is cooked in a solar oven according to the scheme in Figure 1), the loss of raw materials can be significantly reduced. Thus, the permissible level of meat mass loss during conventional cooking is 35 – 40%. By cooking at temperatures below the boiling point (85 – 90 ° C) and increasing the duration of the process by 5 – 7 times, these losses can be reduced to 10 – 15%., I.e., by 2.3 – 4 times, providing significant resource saving.

In most cases, the product reaches culinary readiness most often when the central layer heats up to a certain temperature – pasteurization temperature, for example, for meat and fish 75 – 80 ° C, confectionery 98 ° C, and so on. However, in some cases, this condition is only necessary, but insufficient, since complete culinary readiness is possible after the required holding time.

The total cooking time depends on the multi-stage cooking technology and is different in time (table 2)

Name of dishes Net power of the installation, kW Servings Time in the usual way, min
Naval borsch with meat 3 nine 180
Goulash with buckwheat porridge 4.5 21 110
Duck stew 0.9 8 60

Table 2 – Cooking time

Conventional technology for cooking porridge and frying various products

Cook the porridge with stirring until the cereal absorbs all moisture (when cooking crumbly and viscous porridge) or thickens (when cooking liquid porridge). After that, the surface is leveled, the heating is reduced, the boiler is closed with a lid and the porridge is brought to readiness (evaporated) at a temperature of 90 – 95? C.

The duration of boiling (evaporation) of buckwheat porridge from a fast-boiling core is 1 hour, from fried cereals – 1.5 – 2, from unboiled grains – 4.5 hours. Rice porridge is evaporated for about 1 hour, wheat porridge 1.5, pearl barley – 2 -3 hours.

Starch grain gelatinization temperature – destruction of the native structure of starch grain during cooking is accompanied by swelling. The gelatinization temperature of potato starch occurs at 55 – 65 ° C, wheat – at 60 – 80, corn – at 60 – 71, rice – at 70 – 80 ° C. When frying on heated surfaces, the temperature on the surface of the product at the end of the frying process is 135 ° C (the formation of a dehydrated crust), and in the center of the product – 80 – 85 ° C. This cooking method is called low fat frying. When frying in fat (deep fat), the product is completely immersed in fat heated to 160 – 180 ° C. In this case, the temperature on the surface of the product at the end of the process, as in frying with a small amount of fat, is 135 ° C, in the center of the product – 80 -85 ° C.

Taking into account the complexity of the quantitative assessment of energy consumption for cooking, its insignificant share in the total heat consumption for thermal processes, for example, the everyday life of a decentralized consumer (about 6 – 8%), it is possible and necessary to transfer this area of ​​heat consumption, for the summer period, to the sphere responsibility of renewable energy.

Figure 1 shows a diagram of a solar oven for cooking food, developed at the Design Bureau of Alternative Energy “VODOMET” (Omsk).

Figure 1 – Scheme of a solar oven for cooking food
1 – solar radiation; 2 – solar salt pond; 3 – furnace body (shell); 4 – reflective surface of the building; 5 – cauldron (container) for cooking food

The heat of direct and reflected from the surface 4 solar radiation 1 accumulated by the solar salt pond 2 ensures that the temperature in it is kept close to the temperature of the bottom layer. As can be seen from the diagram, in furnace 3, the temperature with high thermal conductivity of the walls can be close to the temperature of the salt brine of the solar salt pond 2 – 85 – 95 ° C. Oven 3 can be either individually or all together 5 boilers with various products, starting with broths and ending with compote (for a description of the solar salt pond, see the author’s monograph: Osadchy G.B. Solar energy, its derivatives and technologies for their use (Introduction to renewable energy) / G.B. Osadchith. Omsk: IPK Maksheeva E.A., 2010.572 p..).

Of course, for the solar oven, their own technologies for cooking various dishes should be developed, based on the fact that the temperature in the oven in most cases will not reach 100 ° C, which means that the cooking time will increase. For example, to prepare breakfast, the cauldron of meat will need to be put into the oven late in the evening, after which cooking will take place all night without human intervention. In such an oven there is no danger that porridge, pasta or fish will burn or not cook..

The solar oven can be part of the heating equipment of a summer cafe, canteen or restaurant, Figure 2.

Figure 2 (section along A – A of Figure 1) – Scheme of a summer cafe attached to the side of the solar oven for cooking food
1 – solar salt pond, 2 – furnace body (shell), 3 – boiler, 4 – bain-marie, 5 – distribution table, 6 – food intake room of a summer cafe (summer canteen of a children’s health camp, a restaurant with a summer bath)

This architecture (layout) of a trade or public catering enterprise allows you to have significant stocks of ready-made dishes of various assortments, moreover, that have not lost their taste, heated regardless of the time of day and the number of visitors. After all, it is known that when boiled starch-containing products are cooled, the amount of soluble amylose in them decreases as a result of retrograde (precipitation). In this case, aging of starch jellies (syneresis) occurs, the products become stale. The aging rate depends on the type of products, their humidity and storage temperature. The higher the humidity of the dish, culinary product, the more intensively the amount of water-soluble substances in it decreases. The fastest aging occurs in millet porridge, slower, semolina and buckwheat. Temperature rise slows down the retrograde process. Therefore, dishes from cereals and pasta, which are stored in 4 bain-marie with a temperature of 70 – 80? С, will have good organoleptic characteristics within 4 hours. If you put fish, potatoes, porridge, etc. in the proposed oven in the evening, then breakfast will be ready in the morning – including hot water for tea, coffee (in the cooler the water temperature is 95? C).

The solar oven can be used to extract (digest) fat from edible bone – how long does it take? 10 hours, for preparing feed for pets and birds.

The water that has undergone heat treatment in a pipe laid along the bottom of the solar salt pond 1 will be pasteurized, that is, one in which pathogenic bacteria are destroyed, and the vital activity of other microorganisms is significantly suppressed. As you know, the pasteurization effect is predetermined by the heating temperature and the duration of water holding at this temperature. The minimum pasteurization temperature is 63 ° C, and holding at this temperature should be at least 60 minutes. In practice, the pasteurization effect is achieved when water is heated to a temperature of at least 80 ° C and held for 15 – 20 s..

Pasteurized water is intended for washing dishes, cutlery, units and parts of food equipment.

The solar oven can also be used both for numerous types of industrial activities, and for serving a large flow of vacationers, travelers, especially since their main flow is always in the summer..

To satisfy the appetite of gourmets, which, as a rule, are plentiful among vacationers, not with empty wallets, the heliofurner can be used for drying, cooking and smoking cooked, boiled-smoked and semi-smoked sausages, sausages, small sausages, pig smoked products and fish products

The solar oven allows you to provide one of the main stages of the technological process for the production of sausages, canned food, meat and fish products – heat treatment (table 3).

Processing process Process duration, min Working environment temperature,? С Working environment relative humidity,%
Drying 10 – 25 60 – 95 25 – 35
Roasting 30 – 140 75 – 100 10 – 20
Cooking 30 – 100 80 – 85 90 – 100
Smoking 360 – 1440 50 65

Table 3 – Technological operations of heat treatment of sausages and smoked meats

As you can see from table 3, solar energy accumulated in the solar salt pond, like some other, is suitable for the most delicate operations of preparing delicious dishes.

The benefit of preparing delicious dishes is obvious, since the cost of smoked fish, in retail, is 2 times higher than fresh.

The temperature of the working environment for cold smoking is 20 – 45, and for hot smoking 60 – 150 ° C, which allows smoking also using the energy of a solar salt pond.

Timely heat treatment (pasteurization), in which pathogenic microflora is destroyed under the influence of high temperature, helps to prevent spoilage of products, to increase their shelf life. The solar oven can be used to place cream-ripening baths, in which the cream is heated to the temperature of churning it into butter. In the solar oven (chamber), it is possible to carry out vacuum drying in the production of animal feed (meat and bone, meat, blood and bone meal) and technical fats by dry method.

The volumes of products – milk, beer, wine, and others – to be pasteurized are enormous. The efficiency of pasteurization of dairy products at a temperature of 76 ± 2 ° C is 98.3 – 99.5%, and at 82 ± 2 ° C – 99.6 – 99.8%.

Cooking food and feed for animals will resemble the work of modern washing machines, when the main thing is to load plain things (and, for cooking, the necessary semi-finished products), and then everything happens in automatic mode.

Application of the solar furnace in the southern regions

At the oil-extracting factories of Uzbekistan, when processing cotton seeds, meal is obtained as a secondary product, which is sold as a concentrated feed, since it contains over 40% crude protein.

Cotton meal should contain no more than 0.02% free gossypol. Otherwise, when feeding animals, meal can lead to poisoning, since gossypol is a cellular, vascular and nerve poison that causes inflammatory processes in tissues. This toxin affects the heart, liver, kidneys, causes hemorrhages and infiltrates in the affected organs. Cotton meal is recommended to be included in the feed rations of dairy cows, beef cattle and sheep to a limited extent. It is problematic to use meal in feed for pigs, which, like poultry, are sensitive to the toxic manifestations of gossypol. To improve the feed rations of farm animals and poultry, livestock breeders need meal with a low content of free gossypol (up to 0.01%) and fiber (up to 15%). Previously, such meal was obtained in the industrial conditions of the Kokand MZhK on the basis of low-temperature frying of coarsely ground cotton seed meal at 75 – 80 ° C and processing of the pulp using the prepress-extraction method. However, at the same time, the technical and economic performance of the enterprise worsened, due to additional energy consumption.

Therefore, for frying the meal, without deteriorating the performance of enterprises, due to the lack of consumption of organic fuel, it is possible to use a large-sized solar oven for boiling cotton meal, equipped with appropriate mechanization.

The widespread use of solar furnaces in Russia will significantly reduce unnecessary fuel consumption, improve the environmental situation, raise the energy security of the population, the recreation industry and utilities and increase their energy sovereignty.

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