Bob energiya balantalari asoslari. 20 Chapter fundamentalsofenergybalances

Summary

For maximum heat recovery and minimum use of utilities:

1. 
   Do not transfer heat across the pinch
   
2. 
   Do not use hot utilities below the pinch
   
3. 
   Do not use cold utilities above the pinch
   

3.17 HEATEXCHANGERNETWORKS 123

3.17.3 HEAT EXCHANGER NETWORK DESIGN

Grid representation

It is convenient to represent a heat exchanger network as a grid; see Figure 3.25. The process streams are drawn as horizontal lines, with the stream numbers shown in square boxes. Hot streams are drawn at the top of the grid, and flow from left to right. The cold streams are drawn at the bottom, and flow from right to left. The stream heat capacities CP are shown in a column at the end of the stream lines.
Heat exchangers are drawn as two circles connected by a vertical line. The circles connect the two streams between which heat is being exchanged; that is, the streams that would flow through the actual exchanger. Heaters and coolers can be drawn as a single circle, connected to the appropriate utility. If multiple utilities are used, then these can also be shown as streams. Exchanger duties are usually marked under the exchanger and temperatures are also sometimes indicated on the grid diagram.

Network design for maximum energy recovery

The analysis carried out in Figure 3.22 and Figure 3.24 has shown that the minimum utility requirements for the problem set out in Table 3.2 are 50 kW of the hot and 30 kW of the cold utility; and that the pinch occurs where the cold streams are at 80°C and the hot streams are at 90°C.
The grid representation of the streams is shown in Figure 3.26. The vertical lines represent the pinch and separate the grid into the regions above and below the pinch. Note that the hot and cold streams are off-set at the pinch, because of the difference in pinch temperature.

Grid representation
CP

120 3-BOB ENERGIYA BALANTALARI ASOSLARI.

Chimchilab parchalanish
boshqa chimchilashlar, ya'ni foydali chimchilashlar, bu esa muammolarni yanada parchalanishiga olib keladi. Muammoli dekompozitsiyani avtomatik issiqlik almashinuvi tarmog'ini sintez qilish algoritmlarida ishlatish mumkin.
3.17.2 MUAMMOLAR JADVAL USULI
Muammolar jadvali Linnhoff va Flower (1978) tomonidan kiritilgan chimchilash harorati va minimal foydali talablarni aniqlashning raqamli usulidir. U kompozitsion egri chizmalarni yo'q qiladi, agar muammo qo'lda hal qilinsa foydali bo'lishi mumkin. U endi sanoat amaliyotida keng qo'llanilmaydi, chunki chimchilashni tahlil qilish uchun kompyuter vositalarining keng mavjudligi (3.17.7-bo'limga qarang).
Jarayon quyidagicha:
1. Haqiqiy oqim haroratini oraliq haroratlarga aylantiring. Issiq oqim haroratidan minimal harorat farqining yarmini ayirish va sovuq oqim haroratiga yarmini qo'shish orqali rang berish:
DTmin
issiq oqimlar Tint ¼Tact 2
DTmin
sovuq oqimlar Tint ¼Tact þ 2
Haqiqiy haroratlardan ko'ra intervalli haroratdan foydalanish minimal harorat farqini hisobga olish imkonini beradi. Ko'rib chiqilayotgan muammo uchun DTmin ¼ 10°C; 3.3-jadvalga qarang.
2. Har qanday takrorlangan intervalli haroratlarga e'tibor bering. Bular 3.3-jadvalda qavs ichida keltirilgan.
3. Intervaldagi haroratlarni kattalik bo'yicha tartiblang, takrorlangan haroratlarni faqat bir marta tartibda ko'rsating; 3.4-jadvalga qarang.
4. Har bir harorat oralig'iga to'g'ri keladigan oqimlar uchun issiqlik balansini o'tkazing:
n-chi interval uchun:
DHn ¼ XCPcXCPh ðDTnÞ
3.17 ISITILIK OLISH TARMOQLARI 121
Больше информации об этом исходном текстеЧтобы получить дополнительную информацию, введите исходный текст
Отправить отзыв
Боковые панели